Heavenly Chocolate Mousse Cake

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Preparation info

  • Difficulty

    Complex

  • Serves

    8 to 10

Appears in

The Baking Bible

By Rose Levy Beranbaum

Published 2014

  • About
Oven Temperature 450°F/230°C
Baking Time 7 to 10 minutes

Many years ago, when my parents moved from New York City upstate to Grafton, New York, my mother reported with great excitement that they had discovered an amazing bakery in Saratoga Springs called Mrs. London’s. After I had visited the bakery and was treated to an array of just about every fabulous dessert on the menu, this simple mousse cake is the one that I was most moved to re-create. A gossamer soft and delicate sponge cake (biscuit) is cut to fit and line a loaf pan that is then filled with an equally ethereal and deliciously mellow and velvety chocolate mousse.

Plan Ahead The sponge cake (biscuit) can be baked, cooled, and placed in the pan while the chocolate custard is cooling before you complete the mousse. Alternatively, the cake can be made a day ahead.

Ingredients

Light Sponge Cake

Biscuit

VOLUME WEIGHT
Light Sponge Cake (Biscuit) . . .

Special Equipment

For the cake: See Light Sponge Cake (Biscuit)

For assembling the cake: One 8½ by 4½ inch (6 cups) loaf pan | One baking sheet or extra half sheet pan (inverted), lightly coated with nonstick cooking spray

Method

Make the Cake

Make the light sponge cake (biscuit).

Unmold and Cool the Cake

Run the tip of a sharp knife around the sides to dislodge any cake that may have attached itself to the sides of the pan and unmold the cake at once. Slip a small offset spatula under the narrow edge of the parchment to loosen it. Grasp the parchment and gently slide the cake from the pan onto a baking sheet or inverted sheet pan. Cover with plastic wrap lightly coated with nonstick cooking spray. Cool until it is no longer warm to the touch, about 20 minutes.

Make the Templates

Make the templates for cutting the cake into 4 pieces: 1 continuous piece for the bottom and sides, 2 ends, and 1 top. Measure the outside of the pan and transfer the measurements to sheets of paper or card stock. The templates should be slightly oversized to allow for trimming to fit. Cut out the templates.

Make the Chocolate Custard

See recipe.

Beat the Egg White into a Stiff Meringue

In a medium bowl, beat the egg white and cream of tartar on medium-low speed until foamy. Gradually raise the speed to medium-high and beat until soft peaks form when the beater is raised. Gradually beat in the sugar until stiff peaks form when the beater is raised.

Complete the Chocolate Mousse Filling

With the whisk beater, on low speed, beat the chocolate mixture for about 30 seconds, or just until very soft, floppy peaks form when the beater is raised. Gently fold the meringue into the mousse until uniform in color.

Cut the Cake Pieces

Invert the cake onto a wire rack and carefully remove the parchment. Reinvert the cake onto the baking sheet or inverted sheet pan and remove the plastic wrap. Place the templates on top of the cake so that they all fit. Use kitchen scissors to cut out the 4 cake pieces.

Line the Pan with the Cake Pieces

Line the loaf pan with a sheet of plastic wrap cut 2 feet long, with the excess extending past one end of the pan. Lightly coat the plastic wrap with nonstick cooking spray. Carefully insert the bottom and sides piece of cake into the pan, crust side against the pan. Trim the 2 end pieces to fit tightly against the bottom and sides of the cake.

Unmold the Cake

Remove the cutting board and fold back the plastic wrap to uncover the top of the cake. Place a serving plate or the cutting board on top of the pan and invert the cake. Remove the pan. Gently peel off the plastic wrap.

Use a straight-edge knife to slice the cake from top to bottom. Between slices, wipe off the knife to minimize the likelihood of the chocolate mousse spreading onto the cake.

Compose the Cake

Spoon half of the chocolate mousse into the cake-lined pan. With a small metal offset spatula, lightly press the mousse into the pan to ensure that the mousse fills the corners of the cake. Repeat with the rest of the chocolate mousse. If necessary, trim the tops of the cake pieces to be flush with the top of the pan. Place the top cake piece, crust side up, over the mousse filling and trim its edges to fit inside the cake’s side and end pieces.

Fold over the extended plastic wrap to cover the top of the pan. Lightly press down on the cake’s top. Wrap any excess plastic wrap tightly around the sides of the pan. Set a small cutting board or heavy pan large enough to cover the entire top of the loaf pan on top.

Let the cake sit for 3 hours at room temperature for the chocolate mousse to set. The cake cuts best and has the best texture at room temperature.

Store

Airtight: room temperature, 6 hours; refrigerated, 3 days. Do not freeze, because the texture will become less smooth.

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