1. Prepare the Yeast Mixture:

• In a small bowl, warm the milk slightly (it should feel lukewarm, about 110°F or 45°C—if it’s too hot, it may kill the yeast).
• Sprinkle the active dry yeast over the warm milk along with 1 tsp of sugar to help activate the yeast. Stir and let it sit for about 5-10 minutes, until the mixture becomes frothy and bubbly. If you’re using instant yeast, you can skip this step and mix it directly with the dry ingredients.

2. Mix the Dough:

• In a large mixing bowl, combine the flour, salt, sugar, and cinnamon (if using).
• Make a well in the center of the dry ingredients and add the yeast mixture along with the eggs and vegetable oil. Use a wooden spoon or a stand mixer with a dough hook to stir everything together.
• Mix until the dough comes together into a sticky, somewhat lumpy batter (it should be thicker than a pancake batter, but not as firm as bread dough). If the dough is too thick, you can add a little more warm milk, one tablespoon at a time.

3. Add the Fruit (optional):

• Once the dough is mixed, fold in the raisins, currants, or chopped apple if you are using any. These add a bit of natural sweetness and texture to the oliebollen.
• Cover the bowl with a clean kitchen towel or plastic wrap and let it rise in a warm place for about 1 hour, or until the dough has doubled in size.

4. Heat the Oil:

• In a large, deep pan or deep fryer, heat vegetable oil to 180°C (350°F). You need enough oil to submerge the oliebollen, about 3-4 inches deep. If you don’t have a thermometer, you can test the oil by dropping in a small piece of dough—if it sizzles and rises to the surface immediately, the oil is ready.

5. Fry the Oliebollen:

• Once the dough has risen, use a spoon or ice cream scoop to shape balls of dough about the size of a golf ball.
• Carefully drop them into the hot oil, 3-4 at a time (don’t overcrowd the pan). Fry for about 4-5 minutes, turning them halfway through, until they are golden brown and puffed up.
• Use a slotted spoon to remove the oliebollen from the oil and place them on a paper towel-lined plate to drain excess oil.

6. Serve:

• While the oliebollen are still warm, dust them generously with powdered sugar.
• Serve immediately, and enjoy with a cup of hot chocolate, tea, or coffee for a truly festive treat.