4tablespoonsbrown sugarcan also use granulated white sugar
Half grapefruit crosswise and place grapefruit half cut-side down on a paper towel for 5 minutes.
Invert grapefruit and sprinkle 1 tablespoon of sugar evenly over exposed flesh of each grapefruit half. Using a culinary torch, heat sugar until melted and beginning to turn dark amber.
Alternately, if you don't have a culinary torch, preheat broiler to 450. Transfer grapefruit, cut side up, to a rimmed baking sheet lined with foil. Broil the grapefruit until the sugar is melted and beginning to turn dark amber, about 8 minutes. Watch closely to prevent burning. Let grapefruit cool before serving.