Stir in the dry yeast into the warm milk.
Allow standing for a few minutes to dissolve.
Sift the flour and salt into a large bowl.
Stir the yeast mixture and egg into the flour and mix into a smooth batter.
Stir in the currants, raisins and apple.
Cover the bowl, and leave the batter in a warm place to rise until double in size. This will take about 1 hour.
Heat the oil in a deep-fryer or heavy deep pan to 180-190°C.Use two metal spoons to shape scoops of dough into balls, and drop them carefully into the hot oil.
Fry the balls until golden brown, about 8 minutes. The doughnuts should be soft and not greasy. If the oil is not hot enough, the outside will be tough and the insides greasy.
Drain the finished doughnuts on paper towels and dust with icing sugar.
Serve them piled on a dish with more icing sugar dusted over them. Eat them hot if possible.