Instructions: In a medium saucepan, combine sugar, vermouth, lemon and lime zests, and 2 3/4 cups water. Bring to a boil, stirring occasionally. Remove from heat. Set aside to allow lemon and lime zests to steep in mixture, about 10 minutes.

Strain, discarding zests. Pour mixture into a 13- by 9-inch glass baking dish. Freeze for 8 hours or overnight.

Using a sharp knife, cut off tops and bottoms of grapefruits. Remove peel, pith, and outer membranes. Working over a bowl, cut fruit segments from membranes. Squeeze juice from membranes from into bowl; set aside.

Just before serving, remove granita mixture from freezer. Using the tines of a fork, scrape surface of granita so it resembles crushed ice. Transfer granita to serving bowls, and garnish with grapefruit sections and reserved juice.

This recipe yields 8 to 10 servings.

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