Directions

1. 1. Preheat the oven to 375 degrees F.
2. 2. To make the cake: Place the cocoa in a small bowl and whisk in boiling water to form a paste.
3. 3. Combine the chocolate and milk in a saucepan over medium heat. Stir frequently as the mixture warms and the chocolate melts, about three minutes. Remove from heat.
4. 4. Whisk a small amount of the heated chocolate milk into the cocoa paste and then whisk the cocoa paste into the milk mixture. Return to heat, stir for one minute, remove and cool until tepid.
5. 5. In a small bowl of a mixer, cream the sugar and butter together. Beat in the egg yolks one at a time and add the vanilla. Slowly stir in the chocolate mixture. Set aside.
6. 6. Combine the flour, baking powder, salt and baking soda. Using a spatula or a wooden spoon slowly add the flour mixture to the chocolate mixture.
7. 7. In another bowl whip the egg whites to form soft peaks and, using a rubber spatula, gently fold the egg whites into the batter.
8. 8. Butter and lightly flour two 8 inch round cake pans and divide the batter between the two pans. Bake for 45 minutes and cool on a rack for 15 minutes.
9. 9. Gently remove the cakes from their pans and continue to cool.
10. 10. While the cake is baking make the filling: Put the cocoa into a saucepan and pour in the boiling water and place over low heat. Add the sugar and chocolate.
11. 11. Dissolve the cornstarch in the cold water to make a smooth paste. Whisk the cornstarch mixture into the water and chocolate; add the salt and bring it to a boil, stirring constantly. Boil for one minute.
12. 12. Remove the pan from the heat, whisk in the vanilla and the butter and transfer the mixture to a bowl and refrigerate until cool.
13. 13. Make the frosting: In a double boiler, or a bowl over a pot of simmering water, melt the chocolate. Remove from heat and whisk in the butter, one tablespoon at a time, returning to the heat if necessary to melt the butter.
14. 14. Whisk in the hot water all at once and stir until smooth. Whisk in the corn syrup and the vanilla. Refrigerate for up to 15 minutes before using.
15. 15. To assemble the cake: Use a sharp knife to slice each cake into two disks to form 4 layers. Set one layer aside. Place one layer on a cake round or plate.
16. 16. Generously swath the layer with filling. Add the second layer and repeat. Add the third layer. Quickly apply a layer of frosting to the top and the sides of the cake and refrigerate for 10 minutes.
17. 17. Meanwhile, crumble the remaining cake layer into fine crumbs. Apply a second layer of frosting to the cake and sprinkle liberally with crumbs.
18. 18. Serve within 24 hours. Store in a cool place.