Preheat oven to 325°F. Combine first 6 ingredients and turn into a 13" X 9" baking dish (or divide equally into the 2 pie crust s if making the recipe as pie). Combine brown sugar, oats and flour; cut in butter. Spoon over the cranberry mixture (either over the casserole or the pies). Bake for 1 hour. Serve warm, topped with ice cream, if desired.