Beat egg yolks until thick and lemon colored. Add 1/2 cup sugar, flour, butter, orange rind, and juice; mix well. Pour filling into pastry shell. Bake at 450° for 10 minutes. Reduce heat to 350°, and continue baking 25 minutes or until set.
Beat egg whites (at room temperature) until foamy. Gradually add 1/4 cup plus 2 tablespoons sugar, 1 tablespoon at a time, beating until stiff peaks form. Spread meringue over hot filling, sealing to edge of pastry. Bake at 350° for 10 minutes or until golden brown. Chill. Garnish with orange slices, if desired.