Preheat the oven to 350 F. Spray donut pan with nonstick spray.
Combine flour, sugar, baking powder, and salt in a mixing bowl.
Combine milk, lemon juice, vanilla, eggs, and melted butter in a measuring cup.
Slightly beat the egg mixture.
Pour the liquid into the mixing bowl and mix until just combined. Be sure to get all the flour off the bottom of the bowl!
Bake for 30 minutes, until a toothpick inserted into the center of the dough comes out clean.
Cool completely.