Preheat the oven to 375°F (190°C) and thoroughly grease a standard 12-cup muffin tin or line with paper liners.

In a primary mixing bowl, sift together the all-purpose flour, 1/2 cup sugar, baking powder, baking soda, salt, and 1/2 teaspoon cinnamon to ensure aeration and even leavening distribution.

In a secondary bowl, whisk together the whole milk, 1/3 cup melted butter, room temperature egg, and vanilla extract until emulsified.

Incorporate the wet mixture into the dry ingredients using a folding technique with a spatula just until no large pockets of dry flour remain; do not overmix to preserve the fluffiness of the crumb.

Spoon the batter into the prepared muffin cups, filling each approximately 3/4 full to allow for proper expansion and doming.

Bake for 15 to 20 minutes, or until the internal temperature reaches 200°F and a toothpick inserted into the center emerges clean.

Prepare the coating by mixing 1/2 cup granulated sugar and 1 teaspoon cinnamon in one shallow bowl and placing the 1/4 cup melted butter in another.

Allow the muffins to cool in the tin for 5 minutes before removing to prevent structural collapse while still facilitating butter absorption.

Brush or dip the top of each warm muffin into the melted butter and immediately dredge in the cinnamon-sugar mixture until fully coated.