1. Preheat oven to 350° F. Line a muffin pan with cupcake liners. Using an electric mixer, beat together brown sugar and butter in a large bowl until creamy. Add eggs, one at a time, beating well after each one added. Blend in the mashed sweet potato and vanilla. 2. In a bowl, whisk together flour, baking powder and soda, spices, and salt. Add half of dry mixture to the sweet potato mixture, stirring until well combined. Mix in milk and remaining dry mixture. 3. Spoon sweet potato batter into your lined muffin cups, filling ¾ full. Bake for 20–22 minutes, or until a toothpick inserted in the center of each muffin comes out clean.4. Cool the muffin pan on a wire rack for 5–10 minutes, then remove each muffin and cool completely.5. For frosting, whisk together the sugar, egg whites, water, cream of tartar, and salt in a heatproof mixing bowl. Set bowl over a saucepan of simmering water, making sure the bowl does not touch the water. Using an electric mixer, beat for 5–7 minutes until stiff peaks form. Remove the bowl from the heat and beat for 1 more minute. Add vanilla and marshmallow crème, beating until well combined.6. Grab a quart- or gallon-sized Ziploc® bag and a small bowl. Place bag inside, point-side down, and open bag around the mouth of the bowl. Scoop frosting into the bag, pull it out, twist the top, and cut half an inch off the bottom corner of the bag. Using the palm of your hand, squeeze frosting onto muffins, starting on the outside and spiraling inward. When you reach the middle, lift the bag straight up to create a peak.7. Set an oven rack about 6" from the top and pre-heat broiler. 8. Place 4 muffins on a baking sheet and put under broiler. Toast your frosting for about 90 seconds, or until it starts turning brown. Check every 15–20 seconds, repositioning baking sheet to allow even toasting. Repeat with all muffins. Note: You can use a culinary torch instead of the broiler if available.9. Serve these delicious muffins at holiday gatherings—all the flavor of a traditional sweet potato casserole, with a different look and appeal. Enjoy!