01 - Preheat your oven to 375°F. Grease a standard donut pan thoroughly with nonstick spray or butter to prevent sticking.
02 - In a large mixing 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 the mixture is smooth and well combined.
04 - Pour the wet ingredients into the dry ingredients. Stir gently until just combined, being careful not to overmix as this can make donuts tough.
05 - Transfer batter into a piping bag or use a spoon to distribute evenly into donut pan cavities, filling each about three-quarters full.
06 - Bake for 10-12 minutes until donuts are lightly golden and a toothpick inserted into the center comes out clean.
07 - Let donuts rest in the pan for 3 minutes to set, then carefully remove and transfer to a wire rack.
08 - While donuts cool slightly, combine granulated sugar and ground cinnamon in a shallow bowl, mixing thoroughly.
09 - Brush each warm donut lightly with melted butter, then immediately roll in the cinnamon sugar mixture until completely coated.
10 - Serve donuts warm for best texture, or allow to cool to room temperature before serving.