Peel and finely dice the onions. Heat the fat in a saucepan and sauté the onions in it. Briefly sweat the flour and tomato paste in it. Add tomatoes with juice and chop. Stir in 3/4 l water and stock, bring to the boil, simmer for 20 minutes.
Cut the sausages into slices. Heat with peas and pasta in the soup. Season the soup with salt and pepper. Wash, chop and sprinkle the parsley.