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1
Preheat oven to 325 degrees F (165 degrees C). Grease three 9-inch baking pans with cooking spray. Line bottoms with parchment paper; grease paper.
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2
Place 6 ounces chocolate in a small bowl. Pour coffee over the chocolate and whisk until smooth. Let stand until slightly cooled, about 5 minutes.
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3
Whisk flour, 1 cup cocoa powder, baking soda, salt, and baking powder together in a bowl.
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4
Beat eggs in a stand mixer on high speed until lemon-colored. Beat in white sugar, coffee mixture, oil, and vanilla extract gradually until batter is well blended. Add flour mixture alternately with buttermilk, beating well after each addition.
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5
Divide batter evenly among the prepared baking pans.
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6
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Cool in the pans for 10 minutes. Invert onto cooling racks and let cool completely, about 30 minutes.
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7
Pour 2 1/2 cups heavy cream into a small saucepan; heat until it just boils.
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8
Place 20 ounces chocolate in a large bowl; pour hot cream on top and whisk until smooth. Let stand at room temperature, stirring occasionally, until slightly thickened, about 45 minutes. Refrigerate until ganache is set and spreadable, 4 to 5 hours.
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9
Combine 1/4 cup ganache, confectioners' sugar, butter, and 1/2 cup cocoa powder in a stand mixer fitted with a paddle attachment; beat on low speed until smooth. Increase speed to high and beat until buttercream is smooth and silky.
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10
Place one cake layer on a serving plate; spread 1/3 cup ganache on top. Repeat twice more. Spread remaining ganache around the sides of the cake. Refrigerate until set, about 30 minutes.
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11
Spread buttercream over the top and sides of the cake. Refrigerate until set, about 10 minutes.
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12
Pour 1 cup heavy cream into a small saucepan; heat until it just boils.
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13
Place 1 cup chocolate chocolate in a small bowl; pour hot cream on top and whisk until smooth. Drizzle glaze over cake. Refrigerate until glaze firms up, at least 30 minutes.
