1. With a paring knife, make 6 slits from top to bottom of grapefruit, cutting through peel and pith but not into fruit. Remove peel, and reserve fruit for another use. Cut peel lengthwise into 1/4-inch-wide strips. If there is very thick pith, remove some with paring knife, leaving 1/4 inch attached to peel.

2. Bring sugar and 2 cups water to a boil in a large pot, stirring occasionally, until sugar dissolves. Wash down sides of pot with a wet pastry brush to prevent sugar crystals from forming. Add grapefruit peel to boiling syrup, and reduce heat. Cover with parchment, and simmer gently until strips are translucent, about 1 1/2 hours. Let peels cool in syrup, about 1 hour. (Refrigerate for up to 3 weeks.)

3. Place sugar for rolling in a shallow bowl. Using a slotted spoon, transfer peel to a wire rack set on a rimmed baking sheet. Wipe off excess syrup with paper towels, then roll in sugar. Arrange in a single layer on a clean wire rack, and let stand until dry, at least 30 minutes.