Heat oven to 350°F and prepare cake pans.
Mix milk with vinegar and set aside.
Combine flour, sugar, cocoa, baking powder, baking soda, and salt.
Add oil, applesauce, vanilla, and milk mixture. Mix well.
Slowly stir in boiling water. Batter will be thin.
Divide into pans, bake 30–35 mins, test with toothpick.
Let cakes cool fully before frosting.
Make buttercream and spread generously.
