From “The Kosher Baker: Over 160 Dairy-free Recipes from Traditional to Trendy” by Paula Shoyer. Copyright © 2010, Brandeis University Press.
3/4 cup (1 1/2 sticks) parve margarine
16 ounces parve semisweet chocolate, roughly chopped
6 large eggs, separated
1 teaspoon parve unsweetened cocoa
1/2 cup sugar
1/3 cup parve whipping cream
Preheat the oven to 350ºF. Take a 9- to 10-inch spring form pan, trace the bottom onto a piece of parchment, and cut out. Cover the top of the pan bottom with aluminum foil, and then wrap the excess foil under the bottom. Attach the pan sides to the bottom, lock in place, and then unwrap the foil and wrap it up and around the sides of the pan. Rub one tablespoon of the margarine around the bottom and sides of the pan. Place the parchment circle in the bottom of the pan and grease with some of the margarine. Grease the sides of the pan as well.
Place the chocolate and remaining margarine in a heatproof bowl over simmering water (or use a double boiler) and stir often until melted. Remove from heat and add the egg yolks and cocoa and beat with an electric mixer for one minute until thick.
In a separate bowl, beat the egg whites with a hand-held or stand electric mixer on high speed until stiff. Turn the speed down to low, add the sugar a little at a time and, once all the sugar is added, turn the speed up to high for 1 minute. Fold the stiff egg whites into the chocolate mixture. Pour 2/3 of this batter into the prepared pan (reserve the other 1/3 for the mousse). Place the pan in a large roasting pan with sides higher than two inches. Place the roasting pan and cake on the middle rack of the oven. Pour boiling water into the roasting pan, around the cake pan, to reach halfway up the sides of the cake pan.
Bake for 40 minutes. Remove the cake pan from the water bath (leaving the roasting pan with water in the oven to cool enough to remove it safely) and let the cake cool in the pan.
While the cake is baking, prepare the mousse. In a bowl, whip the cream with an electric mixer on high speed until stiff and fold into the reserved batter. Mix well. Place in the refrigerator until the cake cools.
When the cake has cooled, spoon the mousse on top of the cake layer and try to smooth the top as much as possible with a silicone spatula. Place in the refrigerator eight hours or overnight.
To remove the sides of the cake pan, heat a sharp knife and run it all around the cake. Open the spring and remove the sides of the pan. Use a spatula to separate the parchment circle from the foil and slide the parchment and cake onto a serving plate. Store the cake in the refrigerator and then place in the freezer one hour before serving to help you cut perfect slices. Store covered in plastic in the refrigerator for up to three days or freeze up to three months.