325 degree oven. Can use 3 c. cooked sweet potatoes (approximately 8). Scrub them, pierce each several times with a fork and wrap in a paper towel. Place in a circle in the microwave and cook on high until squeezably soft. It will take about 10 minutes or so for 8.
Using canned or whole sweet potatoes; mash sweet potatoes together in a closed zip lock bag with your hands (add maple syrup), or in a large bowl with a potato masher. In large bowl, mix yams and apple pie filling. Place in greased, 2 qt. casserole dish. Heat in microwave for 3 - 5 minutes, then top with marshmallows. Be careful not to put the marshmallows all the way to the edge of the casserole dish as they will puff up and could go over the sides. Bake 30 - 45 minutes or until marshmallows are browned. (I used miniature marshmallows).