In a bowl, mix flour, cocoa powder, sugar, baking powder, baking soda, and salt. Add milk, oil, eggs, and vanilla extract, then mix until smooth. Stir in boiling water.
Preheat oven to 350°F (175°C), pour batter into greased pans, and bake for 30–35 minutes. Cool completely.
Cream butter and sugar until fluffy. Add eggs one by one, then mix in vanilla extract.
Combine flour, baking powder, and salt, then add to the mixture alternately with milk.
Pour into pans and bake at 350°F (175°C) for 25–30 minutes. Cool completely.
Whip heavy cream with powdered sugar until soft peaks form.
Level cake layers evenly.
Stack layers alternating chocolate and vanilla with frosting in between.
Apply a thin crumb coat and chill for 20–30 minutes.
Add final frosting and decorate with ganache and toppings as desired.
