Preheat your oven to 350°F (175°C) and grease a donut pan with nonstick spray.

In a large bowl, whisk together flour, sugar, baking powder, and salt until well combined.

In another bowl, mix milk, eggs, melted butter, and vanilla extract until smooth.

Gently fold the wet ingredients into the dry ingredients until just combined; avoid overmixing for fluffy donuts.

Spoon the batter into the prepared donut pan, filling each cavity three-quarters full.

Bake for 12-15 minutes or until golden brown and springy to touch. Cool on a wire rack before serving.