Mix butter and sugar. Add flour, salt, lemon juice and lemon peel. Stir in beaten yolks of eggs, mixed with milk. Fold in stiffly beaten whites of eggs. Pour into custard cups (about 8) or single dish. Set in pan of water and bake 45 minutes at 375 degrees or until nicely browned on top. When done, each serving will contain delicious lemon custard at bottom, tender lemon cake at top. Grand either warm or cold. Serves 8.