In a large bowl, beat eggs and brown sugar for 3 minutes. Add the peanut butter, butter and milk; mix well. Combine the flour, baking powder and salt; gradually add to sugar mixture, beating just until blended. Stir in the peanut butter cups.
Spread into a greased 9-in. square baking pan. Bake at 350° for 25-30 minutes or until a toothpick inserted in the center comes out clean. Cool on a wire rack. Cut into bars.