Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 3 quart casserole dish.
In a medium bowl, toss together the cranberries, apples and white sugar. Pour into the prepared casserole. Mix together the oats, flour, pecans and brown sugar in the same bowl. Spread evenly over the fruit in the dish. Pinch off small pieces of butter and arrange them on top of the oat mixture.
Bake, covered, for 50 minutes in the preheated oven. Remove the lid and bake for an additional 10 minutes, or until the top is toasted.