01 - Preheat oven to 350°F. Grease two 9-inch round cake pans and line bottoms with parchment paper.
02 - Sift flour, sugar, cocoa powder, baking powder, baking soda, and salt into a large mixing bowl. Whisk until evenly distributed.
03 - Add eggs, milk, oil, and vanilla to dry mixture. Beat on medium speed with electric mixer until fully incorporated and smooth, about 2 minutes.
04 - Slowly pour in boiling water while mixer runs on low speed. Batter will appear thin and watery—this consistency ensures a moist crumb.
05 - Divide batter evenly between prepared pans. Bake for 30-35 minutes until toothpick inserted in center emerges clean. Rotate pans halfway through baking.
06 - Let cakes rest in pans for 10 minutes. Run knife around edges, then invert onto wire racks. Cool completely before frosting, about 1 hour.
07 - Beat softened butter in large bowl until creamy and light, about 3 minutes. Sift in cocoa powder and mix until fully combined.
08 - Add powdered sugar in batches, alternating with milk. Beat on medium-high until smooth and spreadable, 3-4 minutes. Mix in vanilla and salt.
09 - Place one cooled cake layer on serving plate. Spread generous layer of frosting over top. Position second layer on top.
10 - Apply thin crumb coat over entire cake. Chill 15 minutes. Finish with remaining frosting, using offset spatula to create decorative swoops and swirls.