Arrange a rack in upper third of oven and preheat oven to 400°F. Peel, core and quarter 4 medium Royal Gala apples (8 oz. each), and cut them into 1/2-inch cubes. Place in a 13-by-9-inch glass baking dish. Add 1 coarsely chopped medium onion, 2/3 cup light brown sugar, 1/3 cup fresh apple cider or apple juice, 2 Tbsp. peeled, minced fresh ginger, 2 Tbsp. melted unsalted butter, 1 Tbsp. white wine vinegar or rice vinegar and 1 1/2 tsp. mustard seeds. Stir to mix and then spread evenly in dish.
Bake, stirring occasionally, for 1 hour. Stir in 1 cup fresh or thawed cranberries (4 oz.) and bake until cranberries are softened, about 20 minutes. Serve warm or at room temperature with roasted or grilled pork or poultry.