In a large bowl, combine the brown sugar, butter, eggs and vanilla just until blended. Combine the flour, baking powder and salt; add to brown sugar mixture. Stir in chocolate chips.
Spread into a greased 13-in. x 9-in. baking pan. Bake at 350° for 18-20 minutes or until a toothpick inserted near the center comes out clean. Cool on a wire rack. Cut into bars.