1. Heat oven to 350°F. Stir together graham cracker crumbs, 1/4 cup cocoa and sugar in medium bowl; stir in butter, blending well. Press mixture firmly on bottom of ungreased 13x9x2-inch baking pan.
2. Beat sweetened condensed milk, flour, egg, vanilla, baking powder and remaining 1/4 cup cocoa in small bowl. Stir in nuts. Spread evenly over prepared crust. Sprinkle chocolate chips over top.
3. Bake 25 minutes or until set. Cool completely in pan on wire rack. Cut into bars. Store tightly covered at room temperature. Makes 24 to 36 bars.