Beat yolks until thick and lemony about 5-8 minutes. Blend in the juice, lemon peel and butter. Combine sugar, flour, salt and add alternately with milk blending well after each addition. Beat whites until stiff. Fold into batter. Pour batter into a 1-1/2 Qt baking dish. Set in a pan of hot water and bake 50 minutes in a preheated 350°F oven until lightly brown. Serve warm with whipped cream.