Place a buttered 5- to 6-cup souffle or other straight-sided baking dish in a larger baking pan (at least 2 in. deep); set aside. In a deep bowl. whip egg whites on high speed until foamy. Continue to beat, gradually adding 1/4 cup sugar, until whites hold short, distinct peaks; set aside. In another bowl, beat (no need to wash beaters) remaining 1/2 cup sugar, 2 tablespoons butter, peel, and egg yolks on high speed until mixture is thick and lighter in color. Stir in buttermilk, lemon juice, and flour. Add about 1/4 of whites to batter; stir to mix well. Gently but thoroughly fold in remaining whites. Pour batter into souffle dish. Set dish in pan on center rack of a 350° oven. Pour boiling water into pan up to level of batter. Bake until pudding is a rich brown on top and feels firm in center when lightly touched, about 1 hour. Serve pudding hot or cool, scooping portions from bottom of dish to yet the sauce that forms. Accompany with berry sauce and fruit. Serves 6. Per serving: 285 cal. (23 percent from fat); 6 g protein; 7.2 g fat (3.4 g sat.); 52 g carbo.; 117 mg sodium; 118 mg chol. Berry sauce. In a blender or food processor, smoothly puree 2 cups rinsed and drained raspberries (or 1 package, 10 oz., thawed frozen raspberries in syrup) with 3 tablespoons sugar (or to taste) and 1 tablespoon berry-flavor liqueur (optional) such as Chambord or framboise. To remove seeds, rub puree through a fine strainer into a bowl. If making ahead cover and chill up to 2 days.