Preheat oven to 375°F (190°C). Line a mini muffin tin with paper liners.
In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and cinnamon.
In a separate bowl, whisk together milk, egg, and melted butter.
Add the wet ingredients to the dry ingredients and stir until just combined.
Fill the muffin liners about 2/3 full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
While the muffins are still warm, combine the 1/4 cup sugar and 1 tablespoon cinnamon in a shallow dish. Roll the warm muffins in the cinnamon sugar mixture to coat.
Let cool completely before serving.
Notes
Store leftover muffins in an airtight container at room temperature for up to 3 days.