Preheat oven to 375 degrees. Spray standard 12 cup muffin pan with non-stick cooking spray. Place muffin pan on large baking sheet.
Place 5-6 slices of sweet potato into each muffin cup, trimming slices to fit cups.
Combine butter, maple syrup, brown sugar, cinnamon and nutmeg in a heavy small saucepan over medium heat. Bring to a boil, stirring often until sugar dissolves. Add about 1 tablespoon of the mixture on top of the sweet potatoes in each muffin cup. Sprinkle each stack with some pecans.
Cover with foil and bake for 25 minutes or until tender. While stacks are baking make marshmallow creme.
Marshmallow Creme: Combine all ingredients with 2 Tbsp. water in a metal bowl over simmering water. Beat with a handheld mixer for 6-7 minutes, until thick and fluffy.
Remove from water and continue to beat for 1-2 more minutes until somewhat cooled.
Transfer to a piping bag.
Remove muffin pan from oven when done baking. Discard foil. Pipe some marshmallow creme atop each stack.
To toast, place muffin pan back into the oven under the broiler for 50-60 seconds. Time will vary depending on your oven, so keep a close watch until they are browned to your liking. Remove pan from oven. Carefully scoop each stack out of pan onto serving platter. Serve immediately.