Mix the meat with salt, pepper, finely chopped onion, finely chopped celery leaves, egg and rice. Mix well the whole composition, form small balls, cover the plate with cling film and refrigerate for a few hours ( I left overnight).
For the sauce:
Finely chop the onion, put in a saucepan with olive oil and crushed garlic.
Leave it on low heat, put 2 glasses of water and the meatballs taken out of the fridge.
Season, put the tomato paste thin with water, the frozen basil and cover with a lid, simmer for about 20 minutes.
In the meantime, the meatballs are turned on both sides.
At the end, sprinkle with finely chopped parsley.