Preheat your oven to 350°F (175°C) and grease a donut pan.
In a large mixing bowl, whisk together the dry ingredients: flour, sugar, baking powder, cinnamon, and salt.
In another bowl, mix the melted butter, eggs, vanilla extract, and milk until well combined.
Pour the wet mixture into the dry ingredients and gently stir until just combined.
Spoon the batter into the prepared donut pan, filling each donut cavity about 2/3 full.
Bake in the preheated oven for 10-12 minutes or until a toothpick inserted comes out clean.
Allow the donuts to cool in the pan for 5 minutes, then transfer to a wire rack.
Combine cinnamon and sugar in a shallow dish.
While still warm, roll each donut in the cinnamon sugar to coat.
Serve immediately and enjoy.