Jan's Sweet Potato Pie

Not sure if this is a Mello family recipe or not. Jan got it from her sister so it could be a Temple family recipe. Either way, it's a big hit for the holidays.

4 or 5 Sweet Potatoes (cooked, peeled, sliced thin 1/2 in)
3 Baking (Cortland) Apples (peeled, cored, sliced)
3 Tablespoons white sugar
1 1/2 teaspoons cinnamon
1/4 teaspoon nutmeg
brown sugar - not measured, used generously
1 bag large marshmallows

Combine white sugar, cinnamon, & nutmeg, this will be used to sprinkle between the potato/apple layers.
In round casserole dish, layer sweet potato slices and apples.
Sprinkle the dry mixture generously.
Add some brown sugar (I don't measure, just drop some generously).
Add a few thin slices of butter.
Add another layer of potato slices and apples and repeat the above steps.
I end with a layer of potato.
Bake covered for about 30 -35 min at 350 degrees.
Add marshmallows and return to oven uncovered for additional 5 min or until marshmallows are browned.