In a blender or food processor, combine the cranberries, vinegar and garlic. Cover and blend or process for 1 to 2 minutes or until nearly smooth.
Add oil, sugar, salt, dry mustard and black pepper to cranberry mixture. Cover and blend or process about 1 minute more or until well combined. Serve immediately or transfer to a storage container. Cover and store in refrigerator up to 2 weeks. Stir well before serving over mesclun. Makes about 2-3/4 cups (22, 2-tablespoon servings).