Cream butter in a large mixing bowl; add orange rind and 1 cup sugar, beating well. Add 1 egg; beat well.
Sift flour, baking powder, and salt 3 times in a medium mixing bowl; gradually add to creamed mixture alternately with juice and milk, beginning and ending with flour mixture; stir well after each addition. Spread mixture evenly in a greased 15- x 10- x 1-inch jellyroll pan.
Beat 2 egg whites (at room temperature) in a small mixing bowl until foamy; gradually add remaining sugar, beating until well blended. Very gently spread meringue mixture evenly over entire surface of batter; sprinkle with coconut. Bake at 350° for 20 minutes. Remove from oven, and cool completely in pan before cutting with a 2 1/2- x 2-inch diamond-shaped cutter.