01 - Preheat your oven to 375°F. Grease a standard donut pan with nonstick spray or butter.
02 - In a large bowl, whisk together flour, sugar, baking powder, cinnamon, and salt until well blended.
03 - In another bowl, whisk together milk, eggs, melted butter, and vanilla extract until fully combined.
04 - Pour the wet ingredients into the dry ingredients and stir until just combined; do not overmix to ensure tender donuts.
05 - Spoon or pipe the batter evenly into the prepared donut pan, filling each cavity about 3/4 full.
06 - Bake for 10 to 12 minutes, or until the donuts are lightly golden and a toothpick inserted comes out clean.
07 - Allow donuts to cool in the pan for 3 minutes, then carefully transfer to a wire rack.
08 - Combine sugar and cinnamon in a shallow bowl for the coating mixture.
09 - Brush each warm donut lightly with melted butter, then roll in the cinnamon sugar mixture until well coated.
10 - Serve warm or at room temperature for best flavor and texture.