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 inch 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.