Combine the ingredients for doughnut batter: flour, baking powder, sugar, milk, butter, eggs and salt. Let rise, then get out the air bubbles by lightly punching the batter with your hands. Flatten out the batter using a rolling pin, and cut out small dough balls with a circular cookie cutter or the rim of glass. Let rise again, then fry. Fill them with jelly using a pastry bag, then close up the hole. Sprinkle with powdered sugar, and serve at room temperature.