Take the egg, milk, yogurt and butter out of the refrigerator in advance so that they get room temperature. Sift the flour. Rinse the raisins in warm water. To 100 ml of warm milk, add yeast, 1 teaspoon of sugar from the total volume and 2-3 tablespoons of flour. Stir, cover and leave the sponge cake at room temperature for 25-30 minutes.