01 - Preheat the oven to 350°F (175°C). Grease and line two 8-inch (20 cm) round cake pans with parchment paper.
02 - In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, salt, and sugar until evenly mixed.
03 - Add the eggs, whole milk, vegetable oil, and vanilla extract to the dry mixture. Beat on medium speed for 2 minutes until the batter is smooth.
04 - Carefully stir in the boiling water; expect the batter to become thin.
05 - Pour the batter evenly into the prepared cake pans.
06 - Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
07 - Allow cakes to cool in the pans for 10 minutes, then transfer onto wire racks to cool completely.
08 - Beat the softened butter in a large bowl until creamy.
09 - Sift in the cocoa powder and mix until fully incorporated.
10 - Gradually add the powdered sugar alternately with whole milk, beating until smooth and fluffy. Stir in vanilla extract and a pinch of salt. Add additional milk by the tablespoon if the frosting is too thick.
11 - Place one cake layer on a serving plate and spread a layer of frosting over it. Position the second cake layer on top, then cover the top and sides with remaining frosting. Smooth with a spatula.