Preheat the broiler, and line a baking sheet with foil. Slice off the rounded top and bottom of a halved grapefruit (so it will sit flat), and cut into the segments of the fruit so they are easy to scoop out later. Sprinkle the cut tops of the grapefruit with 1 tablespoon maple sugar. Broil the grapefruit for 3 to 5 minutes, until the tops are browned and caramelized. Enjoy warm.