Preheat oven to 350 degrees F. Spray casserole with nonstick cooking spray.
Peel the sweet potato and use a mandoline slicer to thinly slice them. Set aside.
Slice the Granny Smith apples with a mandoline slicer.
Arrange apples and sweet potatoes in an alternating pattern and place in the greased pan.
Combine melted butter, cinnamon, and honey. Drizzle over the top of the apples and sweet potatoes.
Bake at 350 degrees for 30 - 35 minutes or until sweet potatoes are fork tender.
Notes
If you don't have a mandoline, slice the potatoes and apples as thinly as possible with a knife. It may need to bake longer. You could also try using a food processor to get thin slices.