Luscious Chocolate Layer Cake

Directions

1. 1
   Position oven rack in the center of the oven; preheat the oven to 350; butter and flour two 9 x2 inch round cake pans.
2. 2
   Make the cake--Whisk together the cocoa and boiling water in a small bowl until smooth.
3. 3
   Whisk the flour, baking soda, and salt in a medium bowl.
4. 4
   Beat the butter, sugar, and vanilla with an electric mixer on medium speed in a large deep bowl until well blended; the mixture will be dry.
5. 5
   Add in the eggs one at a time, beating well after each addition.
6. 6
   Decrease speed to low and beat in the flour mixture alternately with the sour cream, beginning and ending with the flour, just until well blended.
7. 7
   Add the cocoa mixture and blend well.
8. 8
   Divide the batter evenly between the prepared pans.
9. 9
   Bake for 40 minutes, or until a pick comes out clean; cool the cakes in the pans on wire racks for 20 minutes, then invert cakes onto the racks and remove the pans.
10. 10
    Turn the cakes right-side up and cool completely.
11. 11
    Make the frosting--melt the chocolate with the water in a small heatproof bowl set over a saucepan of about 1 1/2 inches of nearly simmering water, whisking until smooth; transfer to a large deep bowl.
12. 12
    Heat the sugar with the egg yolks in another heatproof bowl over the same saucepan of nearly simmering water, whisking constantly, for about 4 minutes, until the sugar is dissolved and the mixture is warm to touch.
13. 13
    Whisk the sugar mixture into the chocolate mixture, add in the vanilla, and beat with an electric mixer on high speed for 3 minutes, or until the mixture has cooled to room temperature.
14. 14
    Beat in the butter one piece at a time, beating until smooth after each addition.
15. 15
    Assemble the cake--Place 1 cake layer on a serving plate; spread about 1 cup of frosting evenly over the layer.
16. 16
    Top with the remaining cake layer and frost with the remaining frosting; serve cut into wedges.