For the dumplings, whisk butter with the whisk of the hand mixer until foamy. Knead in basil, cheese, egg, flour and salt. Cover the mixture and put it in a cool place. Peel onion and garlic and dice finely. Wash and clean the tomatoes and carve them crosswise. Heat oil in a pot, fry onions and garlic until transparent. Deglaze with broth and stock, season with salt and pepper and bring to the boil.
Add the tomatoes to the stock and simmer covered over a low heat for 5 minutes. In the meantime, form small dumplings from the butter-cheese mixture with wet hands. Lift the tomatoes out of the stock with a skimmer and let them drip off. Add dumplings to the stock and cook over a low heat for 8-10 minutes. In the meantime wash parsley, dab dry and chop finely. Serve the broth and dumplings sprinkled with parsley in plates. Garnish with basil as desired