In a medium saucepan, melt butter over medium heat. Add onion and cook, stirring occasionally, until just softened, about 15 min. Stir in wine and simmer until reduced by half. Add cranberries, 1/2 cup water, the sugar and bay leaf. Bring to a boil. Reduce to a simmer and cook, stirring occasionally, until cranberries are just softened, 18 to 20 min. Remove from heat and discard bay leaf. Stir in mustard. Serve warm or chilled. (Can be made ahead. Store in an airtight container in the refrigerator up to 3 days.) Makes 12 to 14 servings.