Instructions

1. Place 2 sticks unsalted butter in a stand mixer (or large bowl if using an electric hand mixer). Place 3 large eggs, 2 large egg yolks, and 1 cup sour cream on the counter. Let everything sit at room temperature until the butter is softened, at least 1 hour.
2. Arrange a rack in the middle of the oven and heat the oven to 350ºF. Coat 2 (9-inch) round cake pans with cooking spray, then line the bottom of each pan with a parchment paper round. Place 2 1/2 cups all-purpose flour, 1 cup Dutch-processed cocoa powder, 2 teaspoons baking soda, and 1 teaspoon kosher salt in a medium bowl and whisk to combine.
3. Add 1 cup packed light brown sugar and 1 cup granulated sugar to the bowl of butter. Beat on medium speed with the paddle attachment until fluffy, 3 to 4 minutes. Stop the mixer and scrape down the paddle and sides of the bowl. Beat in the eggs and egg yolks one at a time, making sure each is fully incorporated before adding the next. Stop and scrape down the bowl again. Beat in 2 teaspoons vanilla extract.
4. With the mixer on the lowest speed, beat in 1/3 of the flour mixture, then 1/2 cup of the sour cream. Beat in 1/2 of the remaining flour mixture, then the remaining sour cream. Beat in the remaining flour mixture until just combined. Add 1 cup hot coffee and whisk in by hand until just combined.
5. Divide the batter between the cake pans and spread into an even layer. Bake until a tester inserted into the center of the cakes comes out clean, 38 to 44 minutes. Place the cakes on a wire rack and let cool for 20 minutes. Flip the cakes out of the pans onto the rack, discard the parchment, and let cool completely, about 1 hour. Meanwhile, make the frosting.
6. Finely chop 12 ounces semi-sweet or bittersweet chocolate and place in a large bowl. Heat 1 cup heavy cream in a small saucepan over low heat until small bubbles form around the edges, 6 to 8 minutes. (Alternatively, microwave the cream until it begins to bubble, about 2 minutes.)
7. Slowly pour the cream over the chocolate and whisk until the chocolate is melted completely. Add 1 teaspoon vanilla extract and 1/4 teaspoon kosher salt and whisk to combine. Refrigerate uncovered until the ganache sets, about 30 minutes, stirring after 15 minutes to keep the ganache smooth.
8. Using a stand mixer fitted with the paddle attachment or an electric hand mixer, whip the ganache on medium-high speed until fluffy and lightened in color, 3 to 4 minutes. Frost the top and sides of the cake with an offset spatula.