Active time: 20 min Start to finish: 9 1/2 hr (includes cooling and chilling)

Ingredients

　　1 small red onion, chopped (1/2 cup)

　　1 (14- to 16-oz) can whole tomatoes in juice, including juice

　　1 cup fresh or frozen cranberries, coarsely chopped in a food processor

　　2/3 cup sugar

　　1/3 cup cider vinegar

　　2 (4- by 1-inch) strips fresh orange zest

　　1 (4- by 1-inch) strip fresh lemon zest

　　1/4 teaspoon dried hot red pepper flakes, or to taste

　　1/8 teaspoon salt

　　Bring all ingredients to a boil in a 2-quart heavy nonreactive saucepan over moderate heat, stirring and breaking up tomatoes. Reduce heat and simmer, uncovered, stirring frequently, until thick, 20 to 25 minutes. Cool preserves, then chill, covered, at least 8 hours (for flavors to develop).

　　Cooks' note:

　　Preserves can be chilled up to 1 week.