Combine the remaining sugar with the malt powder in a bowl and set aside. Put the oil in a deep-fat fryer and heat to 340°F, or fill a large saucepan one third full with vegetable oil and heat over medium-high heat until a cube of bread dropped in it sizzles and turns golden brown in 30 seconds. Fry the doughnuts, in batches, for 3–4 minutes until evenly golden brown and cooked through, turning them in the oil once or twice. (You will need to moderate the heat between batches according to whether the doughnuts brown too quickly or too slowly.) Using a slotted spoon, remove the doughnuts from the hot oil and roll in the malt sugar to coat.