Sift flour, baking powder and salt together.
Beat egg yolks in large mixing bowl until thick and lemon colored; gradually add sugar, beating constantly, alternately add lemon juice, orange rind and corn oil, a little at a time; then beat in 2 cups sifted dry ingredients alternately with milk, adding flour mixture in 3 additions.
Fold in beaten egg whites, then remaining dry ingredients.
Knead on floured board until smooth.
Pat or roll out to 1/4-inch thickness.
Cut with floured doughnut cutter.
Pour corn oil into sturdy, flat bottomed kettle or deep fryer, filling utensil 1/3 full.
Heat over medium heat (375°F.) or until a 1-inch cube of bread turns brown in 40 seconds.
Fry doughnuts and centers in hot oil, turning once, until golden brown on all sides, about 4 minutes.
Drain on absorbent paper.
If desired, roll in confectioners' sugar.
Makes about 1 1/2 dozen doughnuts and 1 1/2 dozen centers.