Preheat oven to 350 degrees, and spray a 9x13 baking pan with cooking spray. Combine melted butter, sugar, vanilla, and eggs, and mix well. In a second bowl, mix together flour, cocoa, baking powder and salt. Gradually add to the butter mixture, beating well until blended. Spread evenly into your prepared pan. Bake 20-25 minutes, or until brownie begins to pull away from edges and a toothpick comes out clean. Do not overbake!! Once brownies are cool, frost with Chocolate Buttercream Frosting.

While the cake is baking, prepare the frosting! Beat butter and cocoa together, then alternate adding the powdered sugar and milk--1 c. sugar, and 1 T. milk--beating well in between each addition. Add salt and mix well. If the consistency is too wet, add about a tablespoon of powdered sugar at a time until it's the right consistency. If it's too dry, add a tablespoon of milk at a time until it's right. You can also alter the amount of cocoa, if you like it more or less chocolate-y.