In a heavy saucepan combine the cranberries, the brown sugar, the raisins, the pears, the zest, the gingerroot, the red pepper flakes, the onion, the vinegar, the mustard seeds, and the salt and simmer the mixture, stirring occasionally, for 20 to 25 minutes, or until the berries have burst. The chutney keeps, covered and chilled, for 2 weeks. Serve the chutney at room temperature.
