• Preheat oven to 350°F. Generously grease three 8-inch round cake pans with cooking spray. Line the bottoms with parchment paper rounds, then grease again. Lightly dust with cocoa powder and tap out the excess. Take your time with this step, this cake is very moist and needs well-prepared pans.
• In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Add the sugar and whisk again until evenly combined.
• Right on top of dry ingredients add eggs, milk, oil and vanilla. Whisk well to combine until lump-free (just about 30 seconds).
• Add boiling water and whisk just until incorporated. The batter will be very thin.
• Use a food scale to evenly divide batter into prepared cake pans.
• Bake cakes all on the same shelf in the center of the oven for 25-30 minutes or until a toothpick inserted into the center comes out clean.
• Remove from the oven, cool for exactly 10 minutes, then invert onto a cooling rack upside down. Cool completely. Line a plate with plastic wrap and invert the cake from cooling rack onto lined plate. Do this slowly and gently as the cake is very moist. Cover the cake with plastic wrap and freeze for 2 hours. I find this cake is hard to frost if it's not partially frozen. (I like to frost it fully frozen)

Frosting

• Frosting: Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed for 2–3 minutes or until nice and creamy. Scrape down the sides of the bowl as needed.
• Add in the powdered sugar and cocoa powder. Mix on low until just incorporated. It will be very thick! Again, scrape down the sides. Add in the heavy cream, vanilla, and salt. Mix again on low until incorporated.
• Increase the speed to high and beat for 30–60 seconds until the frosting slightly lightens in color and becomes very creamy. If it’s too thin, add a bit more powdered sugar; if it’s too thick, mix in a little more heavy cream. Taste and adjust to your liking, adding a pinch of salt if it’s too sweet. Use immediately to frost the cake.

Decorate

• Spread a tiny bit of frosting at the base of the cake stand to hold a cake in place. Working with just one cake layer at a time, unwrap and place on cake stand. Frost in between. Add another layer, frost in between, and top with the final layer. Frost the cake with remaining frosting. You may have a touch leftover depending on how well frosted you like your cake. If desired decorate sides and edges with chocolate curls. I do this by grating a chocolate bar with a vegetable peeler right over the cake.