Pork Chops in Ginger Ale

2 large onions, sliced 1/4 cup butter, divided 5 (3/4- to 1- inch thick) pork chops 2 tablespoons firmly packed brown sugar 1 tablespoon tomato puree or chili sauce 1 tablespoon all-purpose flour 1 cup ginger ale Salt and black pepper to taste In a skillet saute onions in 1/8 cup butter over medium heat