Preheat oven to 375° F.
Melt butter and chocolate in a large, heavy saucepan over lowest heat.
Off heat, mix in remaining ingredients in order listed, beating well after each addition.
Pour batter into a greased 9"x9"x2" pan and bake 40 minutes until brownies just begin to pull from sides of pan.
Cool pan of brownies upright on a wire rack to room temperature, then cut in 16 squares.