Break up compressed yeast and stir into warm milk. Let stand for a few minutes to dissolve.
Sift flour and salt into a large bowl. Stir in yeast mixture and egg until smooth. Stir in currants, raisins, and apple. Cover the bowl and set in a warm place to rise until doubled in volume, about 1 hour.
Heat oil in a deep-fryer to 375 degrees F (190 degrees C).
Use two metal spoons to shape scoops of dough into 12 balls. Drop them carefully into the hot oil and fry until golden brown, about 8 minutes. Remove doughnuts with a slotted spoon and drain on paper towels.
Dust doughnuts with confectioners' sugar. Transfer to a serving platter and dust with more confectioners' sugar.
Cook’s Note
It's important that the oil stays at the right temperature when frying. If the oil is not hot enough, the outsides of the doughnuts will be tough, and the insides will be greasy.
Editor's Note:
We have determined the nutritional value of oil for frying based on a retention value of 10% after cooking. The exact amount may vary depending on cook time and temperature, ingredient density, and the specific type of oil used.
