01 - Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or ensure it is well-greased.
02 - In a medium bowl, thoroughly whisk together the all-purpose flour, baking powder, baking soda, salt, and ground nutmeg.
03 - In a larger bowl, whisk the melted and cooled unsalted butter with the granulated sugar until they are well combined. Incorporate the room temperature eggs one at a time, beating thoroughly after each addition. Stir in the whole milk and vanilla extract.
04 - Gradually fold the dry ingredients into the wet ingredients until they are just combined. Be careful not to overmix to ensure tender muffins.
05 - Evenly distribute the batter among the prepared muffin cups, filling each approximately 3/4 full.
06 - Bake for 16 to 18 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
07 - Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to finish cooling.
08 - While the muffins are still warm, use a pastry brush to generously coat the top of each muffin with the melted unsalted butter.
09 - In a shallow bowl, combine the granulated sugar and ground cinnamon. Dip the buttered muffin tops into the cinnamon sugar mixture until they are generously coated.
10 - Serve the cinnamon sugar donut muffins warm or at room temperature.