Preheat oven to 180ºC . In large saucepan, over low heat, melt 1 cup chips with margarine; remove from heat. Add biscuit mix, condensed milk, egg and vanilla. Stir in remaining chips. Turn into well-greased 13x9 inch pan. Bake 20 to 25 minutes or until brownies begin to pull away from sides of pan. Cool. Garnish as desired. Cut into bars.