Cut the sausage into slices. Clean and wash spring onions. Finely dice spring onion white. Cut spring onion green into rings. Peel garlic and chop finely. Pour beans into a sieve and rinse.
Heat the oil in a pot. Fry the sausage for approx. 4 minutes while turning it until it is crispy. Add onion white, garlic, bay leaf and thyme and fry for 1-2 minutes, turning the sausage. Add the strained tomatoes, stock and beans and simmer over medium heat for about 5 minutes.
Add spring onion rings and sausage slices to the soup about 3 minutes before the end of the cooking time. Season soup with paprika, salt, pepper and sugar. Remove the bay leaf. Add yoghurt.