Ingredients
1/2 cup (1 stick) unsalted butter, cut into small pieces, plus more for pans
4 ounces unsweetened chocolate, chopped
2 cups granulated sugar
1 1/2 cups all-purpose flour, (spooned and leveled)
3/4 teaspoon baking soda
1/2 teaspoon salt
1/2 cup sour cream
2 large eggs
1 cup strong coffee, cooled
1 package (12 ounces) semisweet chocolate chips, (2 cups)
6 tablespoons unsalted butter, cut into small pieces
1 teaspoon vanilla extract
1/2 teaspoon salt
2 1/2 cups confectioners’ sugar
1/3 cup milk
Preparation
Make cake: Preheat oven to 350 degrees. Butter two 8-inch round cake pans. Line bottom of pans with parchmentpaper rounds; butter parchment. Set pans aside.
Heat butter and chocolate in a bowl set over (not in) a pan of simmering water, stirring occasionally, until almost melted. Remove from heat; stir until completely melted.
In a medium bowl, whisk together granulated sugar, flour, baking soda, and salt. In a large bowl, combine sour cream and eggs; whisk in coffee. Gradually add dry ingredients then chocolate mixture, stirring until just combined. Divide batter equally among prepared pans.
Place pans on same rack in oven; bake, rotating pans halfway through, until a toothpick inserted in the center comes out with a few moist crumbs attached, 30 to 35 minutes. Cool in pans 10 minutes; run a knife along edge of cakes, then invert onto a wire rack to cool completely before frosting.
Make frosting: Heat chocolate and butter in a mixer bowl set over (not in) a pan of simmering water, stirring occasionally, until almost melted. Remove from heat; stir until completely melted.
With mixer on low speed, add vanilla and salt. Gradually add confectioners’ sugar and milk in alternating batches; beat until smooth. Let stand 5 minutes.
To frost cake, place a cake layer bottom side up, on a serving plate (tuck strips of waxed or parchment paper under edge of cake), spread about 3/4 cup frosting over the top. Place the other cake layer on top; cover assembled cake with remaining frosting.
