Blackout Chocolate Cake

1. Prepare Oven and Cocoa Paste

Preheat the oven to 375 degrees. In a small bowl, whisk together unsweetened Dutch-process cocoa and boiling water until smooth to create a cocoa paste.

2. Melt Chocolate with Milk

In a saucepan, gently melt unsweetened chocolate with milk, stirring until combined. Pour this into the cocoa paste and stir to create a chocolate mixture.

3. Cream Butter and Sugar

Cream together sugar and unsalted butter until fluffy and light. Add egg yolks, one at a time, and vanilla, beating well after each addition.

4. Combine Dry and Wet Ingredients

Alternate adding the chocolate mixture and the combined dry ingredients (flour, baking powder, salt, and baking soda) to the creamed butter mixture, stirring just enough to combine.

5. Fold in Egg Whites

Whip egg whites until soft peaks form, then carefully fold them into the batter.

6. Bake the Cake

Prepare two 8-inch round cake pans with butter and flour. Divide the batter between the pans and bake for about 45 minutes. Let them cool for 15 minutes before removing from the pans.

7. Make Chocolate Filling

Combine cocoa, boiling water, sugar, bittersweet chocolate, dissolved cornstarch, and salt in a saucepan. Boil for 1 minute, then remove from heat. Stir in vanilla and butter until smooth, then cool and chill.

8. Prepare Chocolate Frosting

Melt semisweet chocolate and butter over a double boiler, then whisk in hot water, corn syrup, and vanilla until smooth. Refrigerate until spreadable.

9. Assemble the Cake

Slice each cake layer horizontally to create four thin layers. Place the first layer on a cake round or plate, spread with chocolate filling, and repeat with remaining layers. Frost the cake with the chocolate frosting.