Preheat the oven to 350 degrees F. Pour the melted butter into a large bowl then beat in the sugars, cocoa and vanilla. Beat in the eggs one at a time. Combine the flour and baking powder, then mix in to the butter mixture until well combined. Stir in the almonds. Pour the batter into a non-stick 9"x13" baking pan. (Lightly grease pan first if not non-stick). Bake for 20-25 minutes, or until a tooth pick comes out clean when inserted in the middle and removed. Cool completely on baking.
For the frosting, beat butter and vanilla until light. Combine icing sugar and cocoa. Add alternately with milk to the butter mixture, beating well. Spread frosting over brownie. Refrigerate until frosting is set. Cut into squares.
Note: Brownie freezes well. Cut them into squares first, place on a tray and freeze solid, then transfer to a tight-sealed container and freeze.