In a large bowl, combine the flour, brown sugar, baking powder and salt. In another bowl, beat the butter, eggs and vanilla until smooth. Stir into dry ingredients just until combined (batter will be thick).
Spread into a 13-in. x 9-in. baking pan coated with cooking spray. Sprinkle with chocolate chunks and chopped candy bars; press gently into batter.
Bake at 350° for 20-25 minutes or until a toothpick inserted near the center comes out clean. Cool on a wire rack. Cut into bars.