01 - Preheat the oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease thoroughly.
02 - In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, light brown sugar, baking powder, baking soda, salt, and ground cinnamon.
03 - In a separate bowl, whisk together the melted and cooled unsalted butter, large eggs, whole milk, and pure vanilla extract until well incorporated.
04 - Pour the wet ingredients into the bowl with the dry ingredients. Stir gently until just combined; avoid overmixing to ensure a tender texture.
05 - Divide the batter evenly among the prepared muffin cups, filling each approximately 3/4 full.
06 - Bake for 16–18 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
07 - Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to finish cooling.
08 - While the muffins are cooling, combine the granulated sugar and ground cinnamon in a small bowl for the coating. Once the muffins are warm, brush each one with melted butter, then roll or sprinkle generously with the cinnamon sugar mixture to coat.
09 - Serve the cinnamon sugar donut muffins warm or at room temperature.