In a medium bowl, whisk together flour, baking powder, and salt. In a large bowl, whisk together milk, brown sugar, eggs, and vanilla. Slowly whisk dry ingredients into wet ingredients until no flour is visible. Let batter sit 10 minutes before transferring it into a piping bag or ziplock bag.

Pour 1" vegetable oil into a large cast iron pan. Turn heat to medium and heat until a candy thermometer set in oil reads 375°. Cut a ½" hole in your piping bag or ziplock bag and squeeze approximately ¼ cup batter into oil in a circular pattern. Fry until golden on both sides, flipping halfway, 3 to 4 minutes in total. Place on a paper towel lined plate to drain.

Dust with powdered sugar before serving.