01 - Preheat oven to 350°F (175°C). Grease a 12-cup muffin tin or line with paper liners.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon.
03 - In a large bowl, whisk together melted butter and sugar until well combined. Beat in eggs, one at a time, then stir in milk and vanilla extract.
04 - Add the dry ingredients to the wet ingredients and mix until just combined. Avoid overmixing.
05 - Divide the batter evenly among the prepared muffin cups, filling each approximately 2/3 full.
06 - Bake for 18–20 minutes, or 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 the tops (or entire muffin, if desired) in melted butter, then roll in the cinnamon sugar mixture until generously coated.
09 - Serve warm or at room temperature.