Preheat the oven to 175 ℃ / 347°F.
Sift or whisk together the flour, sugar, baking powder, and salt.
In a separate bowl whisk together the milk with the egg, vanilla extract, and cooled melted butter. Whisk together until well combined.
Create a well in the center of the dry ingredients, pour the wet ingredients and fold together until there are no more flour lumps in the mixture.
Grease and flour a metal donut baking tray or a donuts silicone molds.
Bake for 22 to 25 minutes.
Allow to slightly cool before unmolding. You can store them in the freezer for up to 3 months, or in an airtight container in the refrigerator for up to 4 days. Use parchment paper between the donuts if you will be layering them.