01 - Preheat oven to 375°F. Grease a standard donut pan with nonstick spray or butter thoroughly.
02 - In a large bowl, whisk together flour, sugar, baking powder, cinnamon, and salt until evenly blended.
03 - In a separate bowl, whisk together milk, eggs, melted butter, and vanilla extract until smooth and fully incorporated.
04 - Pour wet ingredients into dry ingredients. Stir gently until just combined; avoid overmixing to prevent tough donuts.
05 - Spoon or pipe batter into prepared donut pan cavities, filling each approximately 3/4 full.
06 - Bake for 10-12 minutes until lightly golden and a toothpick inserted into the center comes out clean.
07 - Let donuts cool in the pan for 3 minutes, then carefully transfer to a wire rack.
08 - Combine sugar and cinnamon in a shallow bowl, mixing thoroughly until uniform.
09 - Brush each warm donut lightly with melted butter, then roll in the cinnamon sugar mixture until completely coated.
10 - Serve immediately while warm or allow to cool to room temperature. Best enjoyed fresh.