In medium-sized mixing bowl, combine cornmeal mix, flour, sugar, beaten eggs, and buttermilk. Stir until batter is smooth. Set aside 10 minutes so muffins will form a round top while baking.
Thoroughly grease bottom and sides of a 6-cup muffin tin with vegetable oil cooking spray or grease each cup with 1/2 teaspoon vegetable oil.
Reduce oven temp to 375. Bake 20-25 minutes or until muffins are golden brown and a knife inserted in center comes out clean.
While muffins are baking, prepare sweet potato filling.
Brown Sugar Sweet Potatoes
Wash and pat dry sweet potatoes. Peeling is optional. If not peeling, simply cut off dark spots.
Slice whole sweet potatoes into circles (or wedges if preferred). Should be at least 1/4" thick. Arrange slices in a single layer on bottom of un-greased baking dish. Set aside.
Drizzle 1/4 of melted butter over slices. Flip over to coat both sides. Cover with foil.
After baking cornbread muffins, reduce oven temp to 350. Bake sweet potatoes for 15 minutes.
In a small bowl, combine remaining melted butter, brown sugar and nutmeg. Stir until brown sugar is dissolved.
Remove sweet potatoes from oven. Drizzle with butter and brown sugar mixture. Flip over sweet potatoes to coat both sides.
For soft texture, cover with foil. For firm texture, remove foil. Continue baking 15 minutes OR until tender.
Stuff Cornbread Muffins
Allow muffins and sweet potatoes to cool.
Flip muffins over. Use a teaspoon to carefully remove center without touching top or sides. Save to use as a plug.
Place a teaspoon of mashed sweet potatoes in center. Plug hole with piece of bottom crust.
Flip over and serve muffins as a side dish or dessert.
Place stuffed muffins in muffin tin. Cover with mini marshmallows. Place under broiler for 30 seconds or until golden brown. Watch closely to prevent burning. Serve in a dessert glass or bowl. Cover with sprinkles if desired.