01 - Preheat oven to 375°F. Grease a standard donut pan thoroughly with nonstick cooking spray or melted butter, ensuring all surfaces are coated for easy release.
02 - In a large mixing bowl, whisk together all-purpose flour, granulated sugar, baking powder, ground cinnamon, and salt until evenly distributed and well blended.
03 - In a separate bowl, whisk together milk, eggs, melted butter, and vanilla extract until completely smooth and fully incorporated.
04 - Pour the wet mixture into the dry ingredients. Stir gently with a spatula or wooden spoon until just combined, being careful not to overmix as this will result in dense donuts.
05 - Transfer batter into a piping bag or use a spoon to distribute evenly into the prepared donut pan. Fill each cavity approximately three-quarters full to allow for rising during baking.
06 - Bake for 10 to 12 minutes until donuts are lightly golden on top and a toothpick inserted into the center comes out clean. Avoid overbaking to maintain moisture.
07 - Let donuts rest in the pan for 3 minutes to set slightly, then carefully remove and transfer to a wire cooling rack. They should still be warm for coating.
08 - While donuts are baking, combine granulated sugar and ground cinnamon in a shallow bowl, mixing thoroughly to create an even coating blend.
09 - Brush each warm donut lightly with melted butter using a pastry brush, then immediately roll in the cinnamon sugar mixture, pressing gently to ensure complete coverage on all sides.
10 - Serve immediately while warm for best flavor, or allow to cool to room temperature. Store in an airtight container for up to 2 days.