01 - Preheat oven to 350°F. Grease and flour two 8-inch round cake pans, then line the bottoms with parchment paper for easy removal.
02 - Sift together flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large mixing bowl. Whisk thoroughly to ensure even distribution of leavening agents.
03 - Create a well in the center of the dry ingredients. Add eggs, milk, oil, and vanilla extract. Beat on medium speed with an electric mixer until completely smooth and well incorporated, about 2 minutes.
04 - Carefully pour in boiling water while mixing on low speed. The batter will become thin and glossy—this is normal. Continue mixing until fully combined, about 1 minute.
05 - Evenly distribute batter between the two prepared pans. Bake for 30 to 35 minutes until a wooden toothpick inserted in the center emerges clean or with just a few moist crumbs.
06 - Let cakes rest in pans for 10 minutes to set. Run a knife around the edges, then invert onto wire racks. Peel off parchment paper and cool completely before frosting, about 1 hour.
07 - Beat softened butter in a large bowl until creamy and pale, about 3 minutes. Gradually sift in powdered sugar and cocoa powder, mixing on low speed initially to prevent dust clouds.
08 - Add vanilla extract and salt. Increase mixer speed to medium-high and beat until smooth, about 2 minutes. Add milk one tablespoon at a time until frosting reaches spreadable consistency.
09 - Place one cooled cake layer on a serving plate. Spread an even layer of frosting over the top. Position the second cake layer carefully. Frost the top and sides of the entire cake, using an offset spatula to smooth the surface.
10 - For clean slices, run your knife under hot water and wipe dry between cuts. Serve at room temperature for optimal flavor and texture.