2 1/2 tsp. instant espresso or coffee
2 c. cake flour
3 1/4 c. sugar
3/4 c. unsweetened cocoa
1 1/4 tsp. baking soda
1/2 tsp. baking powder
Salt
8 eggs
1 c. sour cream
1/2 c. oil
2 1/2 tsp. vanilla
15 tbsp. butter
12 oz. semi-sweet chocolate
3 oz. unsweetened chocolate
1 1/2 c. heavy cream

Heat oven to 350 degrees. Butter and flour two 9 inch round cake pans. Dissolve espresso in 1 cup hot water. Cool.

Combine flour, 2 cups sugar, the cocoa, soda, baking powder and 3/4 teaspoon salt. Add espresso, 2 eggs, the sour cream, oil and 1 teaspoon vanilla. Beat on medium speed 2 minutes.

Pour into pans. Bake until cake pulls away from sides of pan, 25 to 30 minutes. Cool on racks 10 minutes. Remove from pans. Cool completely.

Chop 9 ounce semi-sweet chocolate and the unsweetened chocolate. Melt 12 tablespoons butter over low heat. Off heat, stir in chopped chocolate until smooth. Separate remaining 6 eggs. Gradually beat 3/4 cup sugar into yolks. Slowly beat in 1 teaspoon vanilla and the chocolate mixture.

Beat the egg whites with a pinch of salt until they hold soft peaks. Gradually beat in 6 tablespoons of the sugar and continue beating to stiff peaks. Gently fold the whites into the chocolate mixture.

Beat 3/4 cup of the cream until almost stiff and fold into the chocolate mixture. Set aside 4 cups of this mousse. Cut the cakes in half horizontally to make 4 thin layers. Put two layers on separate plates. Spread each with 2 cups of the reserved mousse. Chill until firm, about 20 minutes or freeze 10 minutes. Top each with a second cake layer and refrigerate.

Beat remaining 3/4 cup cream with 1/4 cup sugar and 1/2 teaspoon vanilla until stiff. Spread the whipped cream over one of the layered cakes. Chill until firm, about 30 minutes. Top with the second layered cake. Chill until firm, at least 20 minutes. Stir the remaining mousse to soften and spread over top and sides of cake.

Melt the remaining 3 ounce semi-sweet chocolate with the remaining 3 tablespoons butter over low heat. Drizzle the melted chocolate over the top and around the edge of the cake.