01 - Preheat oven to 350°F. Grease and flour two 8-inch round cake pans.
02 - Sift together flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large mixing bowl.
03 - Add eggs, milk, oil, and vanilla extract. Beat on medium speed until smooth and well combined.
04 - Carefully pour in boiling water while mixing. Continue beating until batter becomes glossy and thin.
05 - Divide batter evenly between prepared pans. Bake for 30 to 35 minutes until a toothpick inserted in the center comes out clean.
06 - Let cakes cool in pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
07 - Beat softened butter until creamy. Gradually sift in powdered sugar and cocoa powder, mixing until fully 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 frosting evenly over top. Position second layer and frost top and sides, smoothing with spatula.
10 - Decorate as desired. Slice and serve immediately or refrigerate until ready to serve.