Preheat your oven to 350F (175C). Grease a standard 12-cup muffin tin generously with butter or nonstick spray.
In a large bowl, whisk together the all-purpose flour, baking powder, salt, and ground nutmeg until evenly combined.
In a separate bowl, whisk together the granulated sugar, vegetable oil, egg, whole milk, and vanilla extract until smooth. Pour the wet mixture into the dry ingredients and stir with a spatula until just combined. Do not overmix.
Divide the batter evenly among the 12 muffin cups, filling each about two-thirds full. Bake for 18 to 20 minutes, until the tops are lightly golden and a toothpick inserted in the center comes out clean.
While the muffins bake, place the melted butter in a small bowl. In another small bowl, mix together the granulated sugar and ground cinnamon.
As soon as the muffins are cool enough to handle, dip the top of each muffin into the melted butter, then immediately roll it generously in the cinnamon sugar mixture until fully coated. Serve warm for the best experience.