Best butter in mixing bowl until Soft and creamy. Slowly add sugar and beat until smooth and well mixed. Beat in egg yolks, 1 at time. Beat until mixture is completely smooth. Add milk, flour, lemon juice and lemon zest. Mix well. Itll OK if batter looks slightly curdled. In bowl beat egg whites until they form soft peaks. Gently fold whites into batter. Spoon batter into ungreased 1-1/2-quart baking dish. Put dish in larger pan and fill larger pan with hot water halfway up sides of baking dish. Bake at 325 degrees about 40 minutes, or until skewer comes out of custard cleanly. Remove from oven and let cool. Serve either tepid or at room temperature with whipped cream. Makes 6 servings. Each serving contains about: 204 calories; 91 mg sodium; 120 mg cholesterol; 7 grams fat; 31 grams carbohydrates; 5 grams protein; 0.01 gram fiber.