In a large bowl, combine the flour, baking powder, and 0.75 cup of the sugar. (If you want a very sweet confection, use a whole cup of sugar.) Stir in the buttermilk, lemon juice, beaten egg yolks, and the grated lemon peel, if using, and set aside. With an electric mixer, beat the egg whites and salt until the whites are stiff. Beat in the remaining half cup of sugar. Gently fold the egg whites into the batter. Spoon the batter evenly into the prepared cups. Pour boiling water into the baking pan until the water reaches halfway up the sides of the cups. Bake for 50 to 55 minutes, until puffy and golden. PER 4.75-OZ SERVING: 229 CALORIES, 6.0 G PROTEIN, 2.6 G FAT, 46.6 G CARBOHYDRATES, .9 G SATURATED FATTY ACIDS, .3 G UNSATURATED FATTY ACIDS, .9 G MONOUNSATURATED FATTY ACIDS, 87 MG CHOLESTEROL, 139 MG SODIUM, .1 G TOTAL DIETARY FIBER Notes: This favorite old-fashioned dessert separates into layers during baking---a tart-sweet pudding on the bottom and a light spongy cake on top. Serve it warm or chilled, plain or with fresh berries, for picnics, potlucks, family meals, or special dinners. Tightly sealed and refrigerated, Lemon Pudding Cake will keep for about 5 days. Prep time: 20 Bake time: 40 50