Heat oven to 350. Grease 13 X 9 X 2" baking pan. Stir together flour, powder & salt. Cut in 3/4 cup butter until mixture resembles coarse crumbs. Beat in eggs & 1/4 tsp. Mint extract, spread in pan. Bake 23-25 minutes or until wooden pick inserted in center comes out clean. In pan over low heat, melt 1/2 cup butter with chocolate chips. Stir in milk & 1/4 tsp. Mint. Pour over baked layer. Let stand until set. Garnish as desired. Refrigerate. Cut into bars.