Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs one at a time, beating well after each addition.

Stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, alternating with the milk, starting and ending with the flour mixture.

Divide the batter evenly between the prepared cake pans.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then turn out onto wire racks to cool completely.

In a mixing bowl, beat the softened butter until creamy.

Add the cocoa powder and mix until well combined.

Gradually add the powdered sugar and milk, alternating between the two, until the frosting reaches a smooth and spreadable consistency.

Stir in the vanilla extract.

Place one cake layer on a serving plate and spread a layer of frosting on top.

Place the second cake layer on top and frost the top and sides of the cake with the remaining frosting.

Slice and serve the cake.