Preheat oven to 350 degrees.
Prepare a 12-slot muffin tin by spraying well with cooking spray.
Prepare cinnamon & sugar mix, and set aside.
In a large mixing bowl, combine flour, brown sugar, baking powder, cinnamon, salt, cream of tarter, and nutmeg, whisking until well combined.
In a smaller bowl, combined melted butter, milk, vanilla, and the egg, and whisk until well combined.
Pour the wet ingredients into the dry ingredients, and mix with a spoon or spatula, until just combined. Don't over-mix the batter. Over-mixing could result in the muffins drying out faster.
Divide the batter evenly between the 12 prepared muffin slots(roughly 3/4 full).
Sprinkle cinnamon & sugar mix onto each muffin, about 1tsp per muffin.
Bake for 20-22 minutes, or until a toothpick inserted comes out clean.
Let the muffins cool in the tin for 5-10 minutes, then move them to a cooling rack. Pulling them out of the tin too soon, could make them fall apart.
Enjoy!