In a bowl, combine butter, sugar, eggs and 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-by-9-by-2-inch baking pan. Sprinkle with milk chocolate candy bar pieces. Bake at 350 degrees for 30-35 minutes or until a toothpick inserted near the center comes out clean (do not over bake). Cool on a wire rack. Chill before cutting.