Melt butter in a saucepan over the stove. Stir in sugar and then eggs, one at a time. Add vanilla. Combine flour, cocoa, baking powder and salt; set aside 1/4 cup. Add remaining dry ingredients to the egg mixture; mix well. Toss Snickers pieces with reserved flour mixture; stir into batter. Transfer to a greased 13×9-inch baking pan. Sprinkle top with chocolate candy bar pieces. Bake 350 degrees for 30-35 minutes or until toothpick inserted near the center comes out clean. (do not over bake) Cool on a wire rack.