Preheat the oven to 350 F. Lightly grease a 12-muffin pan with non-stick cooking spray.
In a large mixing bowl, combine the flour, baking powder, nutmeg and salt. Add the egg, milk and melted butter and whisk together until batter forms.
Pour evenly into the greased muffin pan. Bake in the preheated oven for 13 to 15 minutes. Remove from oven and let cool slightly.
While the muffins are baking, melt the butter in a small bowl. Combine the brown sugar, white sugar, and cinnamon in another small bowl.
Loosen the muffins from the muffin pan and dip the tops into the melted butter, then directly into the cinnamon-sugar mixture. Place back into the muffin pan, or onto a serving plate.
Serve Snickerdoodle Muffins warm, with butter. Enjoy!