Combine flour, eggs, yoghurt, sugar, salt and vanilla sugar in a large mixing bowl. Let the dough sit for 30 minutes, it will rise.
Form the dough into balls with 5cm diameters.
Heat the vegetable oil to 190 degrees C in a large pot or deep fryer over high heat. It is best to use a basket or slotted spoon for deep frying the donuts as the oil will be extremely hot. Deep fry the dough in the oil. Drain on paper towels.