In a small bowl, combine the warm milk and sugar. Sprinkle the yeast over the milk and let it sit for about 5-10 minutes until foamy.
In a large mixing bowl, whisk together the flour and salt. Make a well in the center and add the yeast mixture, eggs, and melted butter. Mix until well combined. The dough will be thick and slightly sticky.
Fold in the raisins (or currants) and chopped apple.
Cover the bowl with a clean kitchen towel and let the dough rise in a warm place for about 1 hour, or until doubled in size.
Heat oil in a deep fryer or large heavy-bottomed pot to 350째F (175째C). The oil should be at least 2 inches deep.
Using two spoons, drop spoonfuls of dough into the hot oil, being careful not to overcrowd the pot. Fry the oliebollen in batches, turning occasionally, until golden brown and cooked through, about 3-4 minutes per side.
Remove the oliebollen with a slotted spoon and drain on paper towels. Dust with powdered sugar while still warm.
Enjoy your meal!