01 - Preheat oven to 350°F. 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 2 minutes until the batter is smooth and free of lumps.
04 - Gradually pour in the boiling water while mixing on low speed. Continue until fully combined. The batter will be noticeably thin — this is expected.
05 - Evenly distribute the batter between the two prepared cake pans, tapping gently on the counter to release any trapped air bubbles.
06 - Bake on the center rack for 30 to 35 minutes. Test for doneness by inserting a toothpick into the center of each layer — it should come out clean.
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 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 until the frosting is fluffy and spreadable.
09 - Place one cake layer on a serving plate and spread a generous layer of frosting over the top. Position the second layer on top, then frost the top and sides of the cake evenly using an offset spatula.