Bring the milk, butter, salt and sugar to a boil, add the flour all at once and stir until combined. Continue stirring over low heat until the mixture forms a ball and leaves a residue on the base of the pan. Transfer to a bowl and gradually stir in the eggs until the dough is very smooth.
Transfer to a piping bag and pipe into rings on small pieces of parchment paper.
Heat the frying oil to 325°F. Add the crullers with the paper to the oil, remove the paper and deep-fry the crullers for 4 minutes, until golden brown on both sides. Remove with a slotted spoon and drain on a wire rack. Dust with powdered sugar before serving.