To prepare chocolate cake: Preheat oven to 300° F.
Whisk together cocoa, oil and coffee; set aside. Sift together flour, baking soda, baking powder and salt; set aside.
Cream together butter and sugar. Add eggs, one at a time, beating to combine, then add vanilla extract. Add the cocoa mixture and mix until thoroughly combined. Scrape side of bowl and then add the sifted flour mixture; mix thoroughly.
Pour into 2 greased and floured 10-inch cake pans. Bake 45 minutes or until a wooden pick comes out clean. Check progress during last half of baking and adjust time as needed for oven variations. Layers will be big so they can be cut as directed later in recipe. Allow cakes to cool 15 minutes in pan; remove from pan and allow to cool completely.
To prepare chocolate mousse: Melt chocolate in top of double boiler over simmering water.
Whip cream until just fluffy; set aside.
Mix gelatin with cold water in top of separate double boiler. Place over hot water and stir to make sure it is completely dissolved.
Beat the eggs with sugar until well blended. At medium speed (so the chocolate does not clump while mixing), pour the melted chocolate into the egg and sugar mixture. Mix a little while, then stop and scrape down bowl. Pour in the well-dissolved gelatin and mix on a low speed a little longer. Fold in the whipped cream until well blended. Chill overnight to set up.
To prepare the pastry cream: Heat milk and cream to a slow boil in a heavy saucepan.
While the milk and cream are coming to boil, mix the sugar and cornstarch. Add the whole eggs, yolks and vanilla and mix until really smooth and mixture has no lumps. After the cream and milk have come to a boil, blend 1 cup of milk mixture into the egg mixture. Then pour the egg mixture into the boiling milk mixture, stirring continuously until it thickens. Remove from heat. Pour pastry cream into a container and place plastic wrap over the pastry cream so it does not form a skin. Refrigerate overnight.
To prepare the frosting: Whip together cream and confectioners' sugar.
To assemble cake: Cut 1 chocolate cake layer into 3 pieces. Pipe chocolate mousse around the first layer, then pipe pastry cream to cover the top of the first layer. Top with second layer of cake. Pipe pastry cream around outside of the second layer, then pipe chocolate mousse to cover the top of the second layer. This is known as checkerboard effect. Top with the third cake layer. Spread the whipped-cream frosting around the entire cake. Sprinkle top with white chocolate shavings and drizzle melted dark or semisweet chocolate lightly over the shavings.
Melt 1 pound dark chocolate or semisweet chocolate in top of double boiler over simmering water.
Cover the back of a flat and smooth cookie sheet with a sheet of parchment paper. Pour melted chocolate on top of the paper; spread and smooth it out over the entire cookie sheet. Chill in the refrigerator until firm.
To garnish cake: Set out chilled chocolate at room temperature 5 minutes. Measure the height of the finished cake plus 1/4 inch. Using scissors, cut the chocolate and the parchment into 2 strips, each the height of the measured cake plus 1/4 inch. Pick up 1 strip with the parchment and wrap around the cake; pull off the parchment once it is in place.Makes 10 Source: