Preheat the oven to 350°F (175°C) and grease a muffin tin.
In a bowl, whisk flour, sugar, baking powder, baking soda, cinnamon, nutmeg, and salt.
In another bowl, mix mashed sweet potato, milk, egg, vanilla, and melted butter.
Gradually fold dry ingredients into wet until just combined.
Divide the batter evenly into muffin cups, filling each ¾ full.
Bake for 22–25 minutes, or until a toothpick comes out clean.
While baking, simmer coffee, maple syrup, butter, cocoa, and sea salt in a saucepan for 5 minutes.
Let muffins cool slightly, then drizzle with the coffee syrup.
Eat immediately or pretend you’ll share them later.