Bring to the boil plenty of water, 3-4 liters, with salt. When it comes to the boil, drop the dumplings into water but not too many at a time - it's better to boil them in 2-3 turns if you have more. Mix carefully with a spoon and, when it starts to boil, reduce the heat to low. Simmer for no more than 3-4 minutes, otherwise they won't stay whole, they will break.
Meanwhile, peel, wash and finely chop the onion and cook it in lots of oil until golden brown.