1. Preheat oven to 350Â° F.
2. Using sharp knife, cut grapefruit in half; cut to free sections and remove fibrous center. Place sections in medium bowl.
3. Peel oranges, cutting deeply enough to remove white pith. Cut between fruit and membrane to loosen sections. Remove seeds; combine orange sections with grapefruit sections, tossing to mix well.
4. Using electric mixer at high speed, beat egg whites, cream of tartar and salt in large bowl until soft peaks form. Sprinkle in sugar, beating until egg whites are stiff.
5. Divide grapefruit and orange sections among four 10-ounce custard cups. Swirl top of each with meringue. Bake for 10 to 15 minutes.