1. Heat oven to 350°F. Grease 13x9x2-inch baking pan.
2. Stir together butter, sugar, flour, cocoa, baking powder, eggs, milk and 1-1/2 teaspoons vanilla in large bowl; beat well. Stir in nuts. Spread batter in prepared pan.
3. Bake 40 minutes or until brownies begin to pull away from sides of pan. Just before brownies are done, in heavy saucepan, melt chocolate chips with sweetened condensed milk and remaining 1-1/2 teaspoons vanilla. Immediately spread over hot brownies. Cool in pan on wire rack. Refrigerate. Cut into bars. Makes 24 to 36 brownies.