Pasteles de Cacao (Cocoa Cakes)

1/2 cup butter
1 cup granulated sugar
3 eggs
3/4 cup cocoa
1 1/2 cups flour
3 teaspoons baking powder
1/8 teaspoon salt
2/3 cup milk
1 teaspoon vanilla extract

Beat butter until creamy. Gradually add sugar, beating until mixture is light and fluffy. Add eggs, one at a time, beating well. Sift together cocoa, flour, baking powder and salt. Add dry ingredients alternately with milk until thoroughly mixed. Mix in vanilla extract. Spoon batter into greased and floured muffin tins. Fill two-thirds full. Bake at 375 degrees F until cake tester comes out clean, about 20 minutes. Do not over-bake. Remove cakes from tins and cool on wire racks.

Serve warm or cold.