Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners.
In a medium bowl, whisk together the all-purpose flour, granulated sugar, baking powder, salt, and ground cinnamon until evenly combined.
In a separate large bowl, whisk together the melted butter, milk, eggs, ground nutmeg, and vanilla extract until smooth and well incorporated.
Gradually add the dry mixture to the wet ingredients while stirring gently until just combined; take care not to overmix.
Evenly divide the batter among the prepared muffin cups, filling each about two-thirds full. Bake for 20-25 minutes or until a toothpick comes out clean.
Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack. Mix 1/2 cup granulated sugar and 1 tablespoon ground cinnamon; dip the tops of warm muffins into this mixture.