01 - Preheat oven to 350°F. Grease and flour two 8-inch round cake pans, lining bottoms with parchment paper for easy release.
02 - Sift together flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large mixing bowl, ensuring no lumps remain.
03 - Add eggs, milk, oil, and vanilla extract to the dry ingredients. Beat on medium speed with an electric mixer until thoroughly combined and smooth.
04 - Carefully pour in boiling water while mixing on low speed. Continue mixing until batter becomes glossy and thin consistency is achieved.
05 - Divide batter evenly between prepared pans. Bake for 30-35 minutes until a toothpick inserted in center emerges clean.
06 - Let cakes cool in pans for 10 minutes before inverting onto wire racks. Cool completely to room temperature before frosting.
07 - Beat softened butter in a large bowl until creamy and light. Gradually sift in powdered sugar and cocoa powder, mixing on low speed until incorporated.
08 - Add vanilla extract and salt. Beat in milk one tablespoon at a time until frosting reaches smooth, spreadable consistency.
09 - Place first cake layer on serving plate. Spread generous layer of frosting over top. Position second layer and frost top and sides evenly, smoothing with an offset spatula.
10 - Decorate as desired with additional frosting swirls, chocolate shavings, or fresh berries. Slice and serve at room temperature.