01 - Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, ensuring even coverage to prevent sticking.
02 - In a large mixing bowl, sift together the all-purpose flour, cocoa powder, granulated sugar, baking powder, baking soda, and salt until uniformly blended.
03 - Add the room-temperature eggs, whole milk, vegetable oil, and vanilla extract to the dry mixture. Beat on medium speed for approximately 2 minutes until the batter is smooth and free of lumps.
04 - Gradually pour in the boiling water while mixing on low speed until fully combined. The batter will appear thin — this is normal and ensures a moist finished cake.
05 - Evenly distribute the batter between the two prepared cake pans, tapping gently on the counter to release any air bubbles.
06 - Bake on the center rack for 30 to 35 minutes, or until a toothpick inserted into the center of each layer comes out clean. Avoid overbaking to retain moisture.
07 - Allow the cakes to rest in their pans for 10 minutes, then carefully invert onto wire racks to cool completely before frosting.
08 - Beat the softened unsalted butter with an electric mixer until light and creamy. Sift in the powdered sugar and cocoa powder, then add the milk and vanilla extract. Beat on medium-high speed for 2 to 3 minutes until the frosting is smooth, fluffy, and spreadable.
09 - Place the first cake layer on a serving plate. Spread an even layer of frosting over the top, then position the second layer on top. Apply frosting evenly over the top and sides of the assembled cake using an offset spatula for a smooth finish.