Preheat the oven to 350°F. Lightly grease a 12-cup muffin tin with baking spray.
In a large bowl, stir together the flour, baking powder, salt, and nutmeg. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the ⅔ cup softened butter and 1 cup of the sugar on medium speed for 2 to 3 minutes.
Add the eggs, one at a time, and mix on low speed until combined. Scrape the bottom and sides of the bowl.
Gradually add the flour mixture to the sugar mixture, alternating with the milk, beating well after each addition.
Fill the prepared muffin cups two-thirds full with the batter.
Bake until golden, 18 to 20 minutes, or until just barely set.
In a medium microwave-safe bowl, melt 2 sticks of butter in the microwave for 1 to 2 minutes.
In a separate medium bowl, combine the cinnamon with the remaining 1 ½ cups sugar.
Dip the baked muffins in the melted butter, coating thoroughly, then coat with the cinnamon-sugar mixture.
Notes
Don't be afraid to use more butter and sugar if desired!