For base: melt 6 tablespoons butter in saucepan. Add remaining base ingredients and mix well.Press mixture into bottom of 8x8 inch baking pan.
For brownies: melt unsweetened chocolate and butter in saucepan. Remove from heat. Stir in sugar until dissolved. Add eggs,one at a time,beating well after each addition. Sift together flour,baking powder and salt. Add to chocolate mixture,mix well. Stir in mint extract.Pour brownie mixture over base. Bake in preheated oven at 350 for 30 to 35 minutes.Cool completely.
For topping:combine all ingredients and beat until smooth.Spread over brownies. Let stand until set.
For glaze: melt chocolate and butter over low heat. Cool. Spread over topping.Let glaze set several hours or overnight before cutting into small squares.