prep: 45 minutes, plus 1 hour 15 minutes chilling
cook: 35 minutes
cool: 30 minutes
cake
Nonstick baking spray
1¼ cups (2½ sticks) unsalted butter, at room temperature
1½ cups granulated sugar
2 large eggs
2 teaspoons pure vanilla extract
2 cups all-purpose flour
⅔ cup unsweetened cocoa powder
2 teaspoons baking soda
½ teaspoon kosher salt
1½ cups hot strong-brewed coffee
2 teaspoons distilled white vinegar
filling
4 tablespoons (½ stick) unsalted butter, at room temperature
¼ cup vegetable shortening
½ teaspoon pure vanilla extract
½ cup powdered sugar, sifted
2 tablespoons whole milk
chocolate glaze
8 ounces bittersweet chocolate baking bars, chopped
8 tablespoons (1 stick) unsalted butter, cut into 8 pieces
1 tablespoon light corn syrup
1. To make the cake: Preheat the oven to 350°F. Heavily spray a 9 × 13-inch baking pan with nonstick baking spray. Line the bottom of the pan with a rectangle of parchment paper and lightly spray the paper.
2. In a stand mixer fitted with the paddle attachment, beat the butter and granulated sugar on medium speed until creamy, about 1 minute. Add the eggs one at a time, beating just until mixed in after each addition. Beat in the vanilla.
3. In a medium bowl, combine the flour, cocoa, baking soda, and salt. Add to the butter mixture, alternating and ending with the coffee, and beat until blended. Stir in the vinegar.
4. Pour the batter into the prepared pan. Bake until a tester inserted in the center comes out clean, 23 to 28 minutes. Cool in the pan on a wire rack for 15 minutes, then place the rack on top of the cake and invert the cake onto the rack to cool completely, about 1 hour.
5. To make the filling: In a stand mixer fitted with the paddle attachment, beat the butter and shortening on medium-high speed until light and fluffy, about 2 minutes. Reduce the speed to low and beat in the vanilla until combined. Gradually add the powdered sugar and milk until thoroughly combined. Increase the speed to medium and beat until fluffy, 2 to 3 minutes.
6. Transfer the filling to a piping bag or a heavy-duty zip-top plastic bag and snip a ½-inch hole in the tip. Set aside.
7. Use a 2½-inch round cutter to cut 12 rounds from the cake. Use a 1-inch round cutter to cut about 1 inch deep into the center of each of the little cakes, taking care not to go all the way through. Carefully remove the centers to leave a 1-inch-deep hole in the center of each cake. Slice off the top ¼ inch of the 1-inch center pieces and set aside to use as lids.
8. Use the piping bag to fill the center of each cake with about 2 teaspoons of filling per cake, leaving a very small space at the top of each one. Place a reserved ¼-inch round cutout on top of the filling of each cake, pressing down lightly to secure. Put the cakes on a wire rack set over a large sheet pan.
9. To make the chocolate glaze: In a 1-quart microwave-safe glass measuring cup (this will make it easy to pour the glaze over the cakes), combine the bittersweet chocolate and butter. Microwave on medium (50%) power in 30-second increments, stirring after each, until melted, 2 to 3 minutes. Stir in the corn syrup and microwave for about 1 minute, stirring every 30 seconds, until the mixture is smooth and glossy.
10. Working quickly, carefully pour the glaze over each cake, smoothing the glaze toward the edges and around the sides using a small offset spatula. Chill the glazed cakes for at least 30 minutes to set.
11. Store in an airtight container in the refrigerator for up to 3 days.
Makes 12 cakes