Cream butter in a large mixing bowl; gradually add sugar, beating well. Add eggs, orange rind, juice, and 2 cups coconut; stir well. Combine flour, baking powder, and salt; stir into creamed mixture.
Spread batter evenly in a greased and floured 13- x 9- x 2- inch baking pan. Sprinkle with remaining coconut. Bake at 350° for 25 to 30 minutes. Cool completely in pan; cut into 2- inch squares.