Lay the bacon strips out on 2 baking sheets. Put into a cold oven. Set the oven to 400 degrees and set a timer for 20 minutes. The bacon will cook as the oven preheats After 20 minutes, check the bacon for doneness. You'll want a crispy bacon for crumbling into the muffins. Add up to an additional 5 minutes if necessary. Once done, remove bacon from pans and transfer to a paper towel-lined plate to drain. Reserve some of the bacon grease on the pans for later. Reduce oven heat to 350 degrees.
Prepare the batter by combining flour, sugar, baking powder, cinnamon, and nutmeg in a large mixing bowl. Stir to combine.
Stir in milk, egg, and bacon grease. Crumble bacon and add to mixture. Pour in melted butter and stir until well combined.
Lightly grease a muffin tin or use cupcake liners. Spoon in enough of the batter to cover the bottom of each muffin tin. Then, spoon a heaping teaspoon of Nutella into each muffin tin. Use the remaining batter to cover the Nutella.
Bake in a 350 degree oven for 20-25 minutes until starting to brown. Remove muffins from tin and cool on a wire rack.