Prepare the Kitchen
Preheat oven to 375°F (190°C). Grease two 6-cup donut pans well with butter or non-stick spray. If you don’t have donut pans, use a muffin tin for donut holes or mini muffins.

Mix Dry Ingredients
In a large bowl, whisk together flour, sugar, baking powder, cinnamon, and salt until evenly combined.

Mix Wet Ingredients
In a separate bowl, whisk milk, eggs, melted butter, and vanilla extract until smooth. Make sure the butter is warm, not hot, to avoid cooking the eggs.

Make the Batter
Add the wet ingredients to the dry ingredients and gently fold together just until combined. A few small lumps are fine, do not overmix or the donuts will be dense.

Fill the Pans
Transfer batter to a piping bag or zip-top bag with one corner cut off. Pipe batter into donut cavities, filling each about ⅔ full to prevent overflow.

Bake
Bake for 12–15 minutes, until the tops spring back when lightly pressed and the edges are lightly golden. Avoid overbaking to keep donuts soft.

Prepare the Coating
While donuts bake, mix cinnamon and sugar in one shallow bowl. Melt butter in another shallow bowl.

Coat and Serve
Cool donuts in the pan for 2–3 minutes, then transfer to a wire rack. While still warm, dip each donut in melted butter, then roll in cinnamon sugar until fully coated.