Pre-heat oven to 350 degrees and grease mini muffin tin with cooking spray.
In a large bowl beat together milk, sugar, vegetable oil, egg, and vanilla until well combined.
In small bowl, mix together flour, baking powder, salt, and nutmeg. Add the dry ingredients to the wet ingredients and stir to combine.
Pour into muffin tins, filling each about 3/4 full.
Bake for about 15 minutes or until tester comes out clean.
Melt the butter in a small bowl in the microwave.
Stir together sugar and cinnamon in another small bowl.
When the muffins are done allow to cool for a few minutes, until you are able to handle them easily.
Dunk the tops of each muffin into the melted butter and then the cinnamon sugar. Set aside to cool.
Video
Notes
These should just get a quick dunk in the butter. If you leave them in too long, they'll soak up too much butter and become soggy + you won't have enough butter for all of the donuts. If it feels illegal to dunk muffins in butter, you can use a pastry brush to brush the butter over the top and then sprinkle with the cinnamon sugar, but we highly (highly!) recommend a quick dip! So good.Store at room temperature for 3-4 days.