Castagnole are small Italian-style doughnut balls that are usually eaten around Carnival time just before Lent. I make them much more often than that because they are so easy and made with 5 ingredients you usually already have!
For deep frying, the perfect temperature of the oil should be between 90 to 100 degrees C. If you do not have a food thermometer, just use a wooden spoon: dip it in the oil and check if it make bubbles. If it does, the oil is ready for deep frying.