For the chocolate cake

1. Lightly coat the insides of two 9 by 1-1/2 inch round cake pans with melted butter. Line the bottom of each pan with parchment paper; then lightly coat the parchment paper with more melted butter. Set aside.
2. Preheat oven to 325 degrees.
3. Place 6 ounces semisweet chocolate and 12 tablespoons butter in a microwave safe bowl and heat for 1 minute. Stir. Continue heating the butter and chocolate mixture in 1 minute increments and stirring until mixture is melted and smooth. Set aside to cool while you beat the eggs.
4. Place the egg yolks and sugar in the bowl of an electric mixture fitted with a paddle attachment. Beat on high until slightly thickened, about 4 minutes. Scrape down the sides of the bowl and beat on high for 2 minutes more.
5. Whisk 3 egg whites until stiff, about 3-4 minutes.
6. Fold the chocolate mixture into the egg yolk mixture with a rubber spatula. Then add a quarter of the egg whites and stir to incorporate; gently fold in the remaining egg whites.
7. Divide the batter between the prepared pans. Bake cakes until tester inserted into center comes out clean, about 25-30 minutes. Cool cakes in pans on rack for 15 minutes. Invert one of the cakes onto the bottom of a 9-inch springform pan. Invert the other cake onto a cardboard cake circle. Remove parchment paper and refrigerate cakes for at least 30 minutes.

For the chocolate strawberry mousse

1. Select 12 of the best-looking strawberries and reserve for the top of the cake. Select 4 ounces of strawberries that are ripe but not usable whole (perhaps smaller or partially damaged). Puree the 4 ounces of strawberries to make 1/2 cup of strawberry puree. Set the puree aside and refrigerate the remaining berries.
2. Place 16 ounces semisweet chocolate, white chocolate and strawberry puree into a microwave-safe bowl and heat for 1 minute. Stir. Continue heating the chocolate mixture in 1 minute increments and stirring until mixture is melted and smooth. Set aside to cool while you prepare the egg whites and cream.
3. In the bowl of a mixer fitted with a balloon whip, whisk the 6 egg whites on high until soft peaks form, about 2 minutes. Continue to whisk on high while gradually adding 2 tablespoons of sugar. Whisk until stiff but not dry, about 30 seconds. Set aside at room temperature until needed. If you are concerned about using raw egg whites in your cake, see the Notes below.
4. Whip the heavy cream until stiff. Fold a quarter of the egg whites into the melted chocolate mixture, then fold in the whipped cream. Now, fold in the remaining egg whites. Set aside at room temperature until needed.

Begin assembly of the cake

1. Assemble the springform pan. Arrange strawberries (not the 12 reserved for decoration) onto the cake layer in the assembled springform pan, stem side down. The berries should be arranged as tightly as possible in the pan. Try to match the heights of the strawberries, trimming down larger berries if necessary. Distribute 3/4 of the mousse over the berries, evenly spreading the top. Holding the pan by the top rim, gently but firmly tap the bottom of the pan 2 to 3 times on your work surface to remove any air bubbles. Add more mousse and tap to settle until the berries are completely covered. You may not need all the mousse – any remaining mousse may be eaten by the chef. Top the mousse with the remaining cake layer and gently press into position. Refrigerate the cake for 2 hours.

For the chocolate ganache

1. Heat the cream, butter, and sugar in a saucepan over medium-high heat. Stir the mixture to dissolve the sugar and bring mixture to a boil. Place the chocolate in a stainless steel bowl. Pour the boiling cream mixture over the chocolate and allow to stand for 5 minutes. Stir until smooth. Cool to room temperature. Keep the ganache at room temperature until ready to assemble the cake.

Complete assembly of the cake

1. Set aside 1 cup of ganache in a pastry bag fitted with a large-sized star tip. Carefully remove the sides of the springform pan. Do not remove the cake from the bottom of the springform pan; this will make the cake easier to handle. Pour remaining ganache over the cake and using an offset spatula, evenly spread the ganache over the top and down the sides. Refrigerate the cake and reserved ganache for at least 1 hour.
2. Remove the cake and ganache from the refrigerator. Pipe 12 evenly spaced stars along the top edge of the cake. Place a strawberry, stem side down, into each ganache star. Refrigerate the cake for 30 minutes before slicing.
3. The Chocolate Strawberry Mousse Cake has a short shelf life. After assembly, this cake can be kept in the refrigerator for no more than 24 hours before serving. Beyond this, the strawberries will begin to weep into the mousse. The cake will still taste fine, but it will not be as appealing to look at.