Steam-Baked Chocolate Layer Cake

Lightly grease two (8-inch) round cake pans with nonstick oil spray and line the bottoms with parchment paper. Arrange the oven racks in positions 2 and 5.

In a medium bowl, sift together the flour, cocoa powder, salt, baking soda, and baking powder. Combine the sugar, buttermilk, oil, eggs, and vanilla in the bowl of a stand mixer with the paddle attachment. Mix on low speed until combined, about 30 seconds. Add the flour mixture to the batter. Mix on low speed until combined, about 30 seconds. Scrape down the sides of the bowl. Pour in the coffee. Mix on low speed until combined, about 30 seconds.

Divide the batter evenly between the prepared cake pans (about 620g in each pan). Tap the full cake pans lightly on the counter once to remove air bubbles.

Transfer the pans to the oven, placing one pan on the left side of rack 5 and the second pan on the right side of rack 2. The pans should not be touching the sides of the oven. Bake, switching the position of the pans halfway through, until the cakes have risen and spring back in the center when gently pressed, about 30 minutes.

Transfer the cake pans to a wire rack and let cool for 20 minutes. Invert each cake onto the rack. Let cool completely.

Clean the stand mixer bowl and paddle attachment. Add the butter to the mixer bowl. Sift the powdered sugar and cocoa powder through a clean fine-mesh strainer into the bowl. Starting on low speed and gradually increasing to medium-high speed, beat the butter mixture until light and fluffy, 3 to 5 minutes. Add the buttermilk, vanilla, and salt. Continue to beat on high speed until the mixture is light and fluffy, 3 to 5 more minutes.

Transfer one cake layer onto a cake stand or platter. Add 1 1/2 cups frosting on top and smooth into an even layer. Place the second cake layer on top. Use the remaining frosting to coat the sides and top of the cake. Decorate and serve.