1. With a sharp knife, cut both ends off grapefruit. Set grapefruit on end on a flat surface and, following the shape of the fruit, cut away and discard peel. Cut sections out from the fruit, leaving the membrane behind.
2. Preheat broiler. Arrange grapefruit sections in 4 shallow ovenproof dishes (such as individual gratin dishes). Sprinkle with brown sugar. Broil until sugar melts and darkens, about 5 minutes (watch carefully). Serve warm, with dollops of yogurt.
Note: Nutrition analysis is per serving.