Mix flour, sugar, baking powder, and salt.
Combine melted butter, milk, egg, and vanilla.
Add wet ingredients to dry ingredients slowly.
Mix until dough forms, don't overmix.
Roll dough on floured surface carefully.
Cut into donut shapes using cutter.
Heat oil to 375°F exactly.
Fry donuts for 2 minutes each side.
Remove when golden brown color appears.
Drain on paper towels immediately.
Dust with powdered sugar while warm.