Preheat oven to 350°F. Grease two 8 or 9 inch cake pans and line with parchment.
Whisk together flour, cocoa powder, baking powder, baking soda and salt. Set aside.
2 cups all-purpose flour, ⅔ cup unsweetened cocoa powder, 1½ tsp baking powder, 1 tsp baking soda, ½ tsp salt
With electric mixer, cream butter and sugar 3-5 minutes until light and fluffy. Beat in eggs one at a time.
3 large eggs
Stir in vanilla.Whisk 1/2 cup milk into cocoa powder until smooth paste forms.
1 cup full-fat milk (warmed), 1½ tsp vanilla extract
Add flour mixture and milk paste alternately in batches to butter mixture, beginning and ending with flour.
Fold gently after each addition just until combined.Divide batter evenly between prepared pans.
Bake 30-35 minutes until toothpick inserted in center comes clean.
Cool in pans 10 minutes before inverting onto wire racks. Cool completely before frosting.
Enjoy this rich, chocolatey sponge cake on its own or top it with chocolate ganache, buttercream, or your favorite frosting!