Remove the fibrous threads of the celery and cut into wedges. Peel the carrot and cut it into pieces.
Melt a lump of butter in a soup pot and fry the onion and garlic until tender. Add the celery, carrot and tomato concentrate and fry for a few minutes. Now add the passata and let it simmer on a low heat.
Add the bouquet garni and the stock to the pan, bring to the boil and let gently simmer for 30 minutes.
Meanwhile, make the meatballs with the ground meat. Season with pepper and salt.
Remove the bouquet garni from the soup and mix the soup finely in blender or with a hand blender. Add the meatballs and let the soup boil for 3 minutes without stirring. The meatballs are cooked when they come to the surface. Season the soup with pepper and salt and serve. Finish with some chopped parsley or a dash of cream.