To prepare Oliebollen: put the mix in a bowl and add the water. Beat until a smooth batter. Mix the currants or raisins into the batter. Cover the batter with a damp cloth and leave in a warm place for about 30 minutes, to raise. Heat your oil to 375°F in a deep frying pan or fryer. Use two spoons to scoop the batter into balls. Fry the balls in the hot oil for 4 minutes until they turn golden, flipping them occasionally to cook them evenly. Drain the Olliebollen on kitchen paper or a colander. Keep them warm in a low oven if you are not serving them immediately. Store in a cool, dry place.