01 - Preheat oven to 350°F and grease a 24-cup mini muffin tin or line with paper liners.
02 - Whisk together flour, sugar, baking powder, baking soda, salt, and cinnamon in a large bowl.
03 - Whisk together milk, vegetable oil, egg, and vanilla extract in a separate bowl.
04 - Pour wet ingredients into dry ingredients and mix gently until just combined. Avoid overmixing.
05 - Divide batter evenly among muffin cups, filling each about ¾ full.
06 - Bake for 10 to 12 minutes until a toothpick inserted into the center comes out clean.
07 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack.
08 - While muffins are still warm, dip tops in melted butter, then roll in cinnamon sugar mixture to coat thoroughly.
09 - Serve warm or at room temperature.