01 - Preheat your oven to 375°F. Grease a standard donut pan thoroughly with nonstick spray or butter.
02 - In a large bowl, whisk together flour, sugar, baking powder, cinnamon, and salt until evenly distributed.
03 - In a separate bowl, whisk together milk, eggs, melted butter, and vanilla extract until completely smooth and well combined.
04 - Pour the wet ingredients into the dry ingredients. Stir gently until just combined; the batter should remain slightly thick. Do not overmix.
05 - Spoon or pipe the batter evenly into the prepared donut pan cavities, filling each about 3/4 full to allow for rising.
06 - Bake for 10 to 12 minutes, or until the donuts are lightly golden and a toothpick inserted into the center comes out clean.
07 - Allow the donuts to rest in the pan for 3 minutes, then carefully transfer them to a wire rack.
08 - Combine 1/2 cup granulated sugar and 1 tablespoon ground cinnamon in a shallow bowl, mixing thoroughly.
09 - Brush each warm donut lightly with melted butter, then roll in the cinnamon sugar mixture until completely coated on all sides.
10 - Serve immediately while warm, or allow to cool to room temperature. Best enjoyed fresh.