01 - Preheat oven to 375°F. Grease a standard donut pan thoroughly with nonstick spray or butter.
02 - Whisk together flour, sugar, baking powder, cinnamon, and salt in a large bowl until evenly distributed.
03 - In a separate bowl, whisk milk, eggs, melted butter, and vanilla extract until fully incorporated.
04 - Pour wet ingredients into dry ingredients. Stir gently until just combined, being careful not to overmix.
05 - Spoon or pipe batter into prepared donut pan, filling each cavity approximately three-quarters full.
06 - Bake for 10 to 12 minutes until donuts are lightly golden and a toothpick inserted comes out clean.
07 - Let donuts rest in pan for 3 minutes, then carefully transfer to a wire rack.
08 - Mix granulated sugar and cinnamon in a shallow bowl until well combined.
09 - Brush each warm donut lightly with melted butter, then roll in cinnamon sugar mixture until completely coated.
10 - Serve immediately while warm or allow to cool to room temperature.