Chocolate Mousse Cake with Galaxy Mirror Glaze

This pastry school assignment was a total surprise. My father, who has enjoyed our family’s traditional cake for the last 84 years, has declared that he wants this cake for his 85th birthday! This cake is packed with flavor and fun textures. Make sure you do ahead as it will need to be frozen overnight before adding the mirror glaze.

Chocolate Mousse Cake with Galaxy Mirror Glaze

  • Servings: 8-10
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Devil’s Food Cake
1 cup (125 g) cake flour
2 T + 2 tsp (20 g) cocoa powder
(2.6 g) Diamond Crystal kosher salt
1 tsp (4 g) baking powder
1/2 tsp (2.6 g) baking soda
1/3 cup (74 g) shortening
7/8 cup (167 g) granulated sugar
1/3 cup (84 g) whole milk
1/3 tsp (1.66 g) vanilla extract
1/4 cup (63 g) whole milk
3 oz (84 g) large eggs*

*A large egg weighs around 1.75 oz. (50 g), but weights will vary depending upon the egg. You’re going to want to weigh your eggs for this cake. To do that, beat two eggs together and while it’s on the scale, remove small amounts until you reach 3 oz or 84 g.

Preheat oven to 350°F. Prep two 8” cake pans by spraying with pan spray and cutting out a parchment circle for the bottom.

Holding a fine mesh colander over your mixing bowl, sift all the dry ingredients into the bowl. Add the shortening and the first milk (1/3 cup/84 g).

Using the paddle attachment, mix at low speed for 7-8 minutes. Because this is a high fat cake, it is important to stop the mixer several times to scrape down the bowl and paddle.

In a separate bowl, combine the remaining milk, vanilla and eggs.

With the mixer running, add this mixture to the batter in three parts. After each part, turn off the mixer and scrape down the bowl. Once the liquids have been fully added, continue mixing for a total of five minutes. The finished batter will be pourable.

Scraping down the sides is an important step
The batter will be pourable after five minutes in the mixer

Divide the batter evenly between the two prepared cake pans (My technique: put an empty bowl on the digital scale and zero it out. Add the batter and note the weight. Divide in two and note that number. Leaving the batter on the scale, spoon out the halved amount into the first cake pan and put the remaining in the second).

Give the pans several sharp raps on the counter to free any large air bubbles. Bake for 25-30 minutes until the center springs back lightly to the touch and a toothpick inserted into the center comes out clean or with a few moist crumbs.

Cool in the pans for 10-15 minutes and then remove and cool on rack completely.

See Mousse Cake Assembly instructions below.

Chocolate Mousse

4-1/3 cups (1000 g) heavy whipping cream         
3-1/2 cups (600 g) semisweet couverture chocolate*
5.6 oz (160 g) egg yolks (from large eggs) (weight measurement is best for this)
2/3 cup + 1 T (140 g) sugar
2-1/3 tsp (15 g) corn syrup

*A good couverture chocolate is what you want here rather than chocolate chips.  Unlike regular chocolate, couverture contains cocoa butter and no other fats. My go-to is Callebaut since I can readily buy it in chunks at our local market. Valrhona, Lindt, Felchlin, Scharffen Berger and Guittard are also excellent brands.

Step 1:
Chop chocolate finely and set in a bowl over a bain marie (double boiler), making sure the bottom of the bowl doesn’t touch the water (an inch of water in the pot is perfect). Set the heat on low and stir the chocolate occasionally until fully melted.  Once melted, set the chocolate bowl on a dishtowel on the counter to cool slightly. Don’t put it straight on the counter because it will lower the temperature too quickly and cause a chocolate chip affect in your mousse. Keep the water on a simmer because you may need it again.

Step 2:
Whip the heavy cream until soft peaks form and then transfer the whipped cream to another bowl. Wash the mixer bowl and whisk attachment and thoroughly dry to get ready for the yolk mixture.

Step 3:
Combine sugar and corn syrup in saucepan and add just enough water to make it look like wet sand and no more. Heat it on medium high heat but do not stir. You’ll want to avoid crystallization of sugar on the sides of the pot, so to do this, dip a basting brush in water and “paint” the sides in downward strokes, making sure not to touch the sugar syrup itself. Cook on medium heat until the syrup reaches 240°F (softball stage) (probe thermometers are great here).

Step 4:
Put the egg yolks in your mixer and whip on low speed. After your sugar mixture reaches 240°F, gently pour it into the mixer, making sure the syrup falls into the yolk mixture and not onto the edge of the bowl. Once it is fully incorporated, turn up the mixer speed to high and whip until tripled in volume and the bowl is cool when you feel the bottom on the outside. (This can take a while. I’ve found 90°F to be perfect).

“Lighten” the chocolate with a little of the yolk mixture to start with.
Be very gentle with folding the rest, but still make sure it’s fully incorporated

Step 5:
Add a spoonful of the yolk mixture to chocolate and stir. This will “lighten” the chocolate and loosen its texture for folding. Fold in the rest of the yolk mixture.

Troubleshooting: If the temperature of the chocolate and/or the yolk mixture aren’t at room temperature, you might find the chocolate seizing up and you’ll have a freckled chocolate. The mixture should be smooth at this point; if not, return it to the mixer and use the whipping attachment for a minute or so until it looks like soft chocolate frosting.

Step 6:
Fold in the whipped cream in parts, being careful not to be gentle and not overmix. When fully incorporated it will be ready for the cake.

Note: If making this to serve on its own, spoon the mousse into dessert cups/bowls at this point and chill for 30 minutes before serving. Top with whipped cream and enjoy! (Mousse can stay fresh for up to five days in the fridge).

See Mousse Cake Assembly instructions below.

Stabilized Whipped Cream
1-1/2 cups (340 g) heavy whipping cream, cold
1/2 cup (51 g) powdered sugar
1 tsp (3 g) gelatin powder (I use Knox brand)
1-1/2 T (22 g) cold water
1 tsp (4 g) vanilla extract
1 tsp (5 g) heavy cream

(I added this whipped cream adaptation after my mousse came out with small freckles of chocolate the first time I made it, (see notes on temperatures when mixing the egg yolk mixture with the chocolate). It was still delicious but it made the cake surface rough; not what you want for a mirror glaze! I decided to add a whipped cream to make the surface smooth for the glaze, and the stabilizer component (the gelatin) to give the whipped cream longer life since the cake was going to be eaten over several days. You can opt not to include it, but my tasters found it added a delicious balance to all the chocolate!)

Place your mixer bowl in the fridge to get cold.

In a small bowl, sprinkle your gelatin over the water and let it bloom for five minutes. Then put it in the microwave for 5 seconds to melt it (give it another few seconds if any unmelted gelatin is visible).

Add the tsp of heavy cream and mix. If the gelatin is too cold, heat again until melted (5 seconds).

When your mixing bowl is nice and cold, whip your heavy cream on medium speed until foamy (15 seconds or so). Add the powdered sugar and vanilla and continue mixing on medium speed until you reach soft peaks.

Turn your mixer to low and drizzle in the gelatin. Continue mixing on medium speed until your peaks are firm and holding their shape, but don’t overmix. I like to finish whipping mine by hand so it looks creamy rather than like butter.

Spread it on the frozen mousse cake and return to freezer. If you have a bench scraper, hold it vertically and scrape it on the side so that the surface is nice and smooth. Once finished with the sides, smooth the top from the edges toward the center.

Assembly: Preparing Cake for Freezer
Place one 8” layer in the center of a 10” cardboard cake round. Using an icing spatula, spread a half inch of the chocolate mousse evenly over it. Top with the second cake and repeat with another half inch of mousse.

Place a 9” spring form pan ring (or a 9” cake ring which doesn’t have a bottom) around the cake so that the cake sits in the center of it. There should be a 1/2″ space between the sides of the cake and the inner edge of the 9″ cake ring. Using a piping bag or a spoon, fill this space all around the cake with more mousse.

Using a long knife, scrape along the top of the ring so it is totally even. Top it loosely with plastic wrap and place the cake and ring in the freezer overnight. It is important for the cake to be frozen completely solid before pouring on the mirror glaze, so plan accordingly.

The next day, remove the cake and remove the springform ring or cake ring (whichever you’ve used). (Heating the sides for a few seconds with a culinary torch makes for easy release).

If adding the stabilizer whipped cream layer, evenly add a half inch layer on both the top and sides and return to the freezer for a few hours.

Smooth out the top and sides and if there are any gaps or holes fill them in as much as possible. (Clean warm fingers work great for fixing small blemishes).

Remove the cake from its cardboard bottom and set it on a 6” cake pan (or on a large can or container that is smaller than 8” round). Center both on a clean sheet pan. (This will catch the drips when you pour on the mirror glaze. Make sure the pan is clean because you can reuse extra glaze).

Pour the mirror glaze over your frozen cake in a smooth, continuous pour over the top of the cake until it starts running down the sides. You have to be fast with any touch ups!! Have a toothpick ready to pop any bubbles before they set.

Galaxy Mirror Glaze
1 T + 2 tsp (15 g) gelatin powder (I use Knox brand)
1-1/2 T cold water

1/2 cup (113 g) water
2 tsp (8 g) vanilla extract
1/2 cup (150 g) sweetened condensed milk
1-1/8 cup (225 g) granulated white sugar
1-1/2 cups (263 g) white chocolate, chopped fine
Food gels (I used blue, purple and red but feel free to experiment!)

Chop the white chocolate and set it aside in a bowl.

Sprinkle the gelatin over the cold water and stir to moisten. Set it aside while you heat the liquids.

In a small pot, bring the water, sugar, condensed milk and vanilla to a gentle simmer. Turn off the heat and stir the bloomed gelatin into the mixture until fully dissolved. Pass this mixture through a sieve.

Pour this mixture over the white chocolate, stirring gently until it melts and is smooth and uniform. Do NOT whisk. It may take up to five minutes to fully melt.

The target temperature for the mirror glaze is 92°F, or anywhere between 90°F and 94°F. While it cools, stir the chocolate periodically to prevent a thick layer from forming on the top.

For a galaxy glaze or for a marbled look with any color combination, divide the glaze into separate containers and add 3-5 drops of food gels in your color choice. Mix well.

Right before pouring the glaze on the cake pour the colors into the same container and swirl gently.

When the glaze is between 90°F and 94°F, it is ready to pour over the frozen cake.

Before the pour. Make sure the glaze is around 92F and that the surface of the cake is smooth.
It’s great fun to watch it come to life as you pour!

Once the mirror glaze has set, gently use a knife or spatula to scrape off the excess glaze dripping from the bottom edge. Place the cake on a larger cake board or platter.

Do not freeze once the glaze has been put on. Do keep it chilled in the fridge for a few hours so that it defrosts before slicing and serving.

Another fabulous mirror glaze for this cake is a Chocolate Mirror Glaze.

Some great special effects:
Have luster dust ready on a basting brush and flick it on the top before it dries. (Not pictured). It’s available in many different colors both online and at any store that carries cake decorating supplies.

Pour a second color mirror glaze right over the top of the first and then immediately scrape it with a spatula (creates a spider vein effect).

Adapted from a recipe from the Auguste Escoffier School of Culinary Arts.

5 thoughts

    1. Thanks so much!! What’s also great about it is you can make the components separately for different desserts. I’ve already made a cupcake version of the cake and a chocolate mousse dessert with whipped cream. Comfort food on a whole new level during rocky times.

  1. Keep on keepin’ on. YOU are amazing, patient, clever, and a wizard in the kitchen. All I can say (after all that) is a resounding WOW!! Can’t wait for the next creation.

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