4 eggs, separated
1/3 cup lemon juice
1 teaspoon lemon zest
1 tablespoon butter
1 1/2 cups granulated sugar
1/2 cup sifted all-purpose flour
1/2 teaspoon salt
1 1/2 cups milk

Preheat oven to 350 degrees F.

Beat together egg yolks, lemon juice, lemon rind, and butter or margarine until thick and lemon colored.

Combine sugar, flour, and salt; add alternately with milk to the yolk mixture, beating well after each addition.

Beat egg whites until stiff. Blend egg whites into batter on low speed of electric mixer. Pour into an 8-inch square baking dish.

Place a pan of hot water in the oven, and set the baking dish into the pan. Bake for 45 minutes.