Savory Sweet Potato Muffins with Bacon

Preheat oven to 350 degrees F (175 degrees C). Grease 12 muffin cups with butter. Line a baking sheet with aluminum foil. Place sweet potato and bacon on the prepared baking sheet. Bake in the preheated oven for 20 minutes; flip sweet potato and bacon. Bake until sweet potato is tender and bacon is crisp, about 20 more minutes. Let bacon cool on paper towels. Heat oil in a skillet over medium heat; cook and stir onion until soft and translucent, about 10 minutes. Whisk flour, baking powder, baking soda, curry powder, and salt together in a large bowl. Stir in Cheddar cheese until coated. Peel sweet potato and transfer to a bowl; roughly mash. Measure out 1 cup of mashed sweet potato. Chop bacon and stir into onion. Whisk eggs vigorously in a separate bowl. Add milk, sour cream, and butter; whisk until smooth. Fold in 1 cup sweet potato, bacon, and onions. Gently stir the sweet potato mixture into the flour mixture, using a rubber spatula, until just combined. Pour batter into the prepared muffin tin. Bake in the preheated oven until a toothpick inserted in the center of a muffin comes out clean, about 18 minutes. Cool muffins in the pan for 5 minutes before removing to a wire rack to cool completely.