For the cake:
1/2 cup unsweetened Dutch−process cocoa, or Hersheys European
2 Tablespoons boiling water
2 ozs. unsweetened chocolate (2 squares), chopped
3/4 cup milk
2 cups granulated sugar
2 sticks unsalted butter, slightly softened
2 Tablespoons unsalted butter, for cake pans
4 eggs, separated
2 Teaspoons vanilla extract
2 cups all−purpose flour, + 1 Tablespoon for pans
1 Teaspoon baking powder
1 Teaspoon salt
1 Teaspoon baking soda

For the filling:
1 Tablespoon unsweetened Dutch process cocoa, + 1−3/4 teaspoons
2 cups boiling water
3/4 cup sugar, + 3−1/2 teaspoons
1 oz. bittersweet chocolate, chopped
2 Tablespoons cornstarch
1 Tablespoon cold water
1/4 Teaspoon salt
1 Teaspoon vanilla extract
2 Tablespoons unsalted butter

Frosting:
12 ozs. semisweet chocolate, chopped
3/4 cup unsalted butter
1/2 cup hot water
1 Tablespoon corn syrup
1 Tablespoon vanilla extract|Preheat the oven to 375 F. To make the cake, place the cocoa in a small bowl
and whisk in boiling water to form a paste. Combine the chocolate and milk
in a saucepan over medium heat. Stir frequently as the mixture warms and the
chocolate melts, about 3 minutes. Remove from heat. 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. 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. 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. In another bowl, whip the egg whites to form soft
peaks and, using a rubber spatula, gently fold the egg whites into the
batter. 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. Gently remove the cakes from their pans and continue to cool. 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.
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. Remove the pan from the
heat, whisk in the vanilla and the butter and transfer the mixture to a bowl
and refrigerate until cool. Make the frosting: In a double boiler (or a pan
within a pan), 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. 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. 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. 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. Meanwhile, crumble
the remaining cake layer, into fine crumbs. Apply a second layer of frosting
to the cake, sprinkle liberally with crumbs and serve within 24 hours. Store
in a cool place.