In a large saucepan, heat the olive oil over medium heat.
Stir in onion, garlic, leeks and thyme and ‘sweat’ (which means cooking very gently without browning), stirring often, for 10 minutes.
Add the stock and bring the soup to a boil. Reduce the heat and simmer for 15 minutes.
Add the beans and the sausage slices and simmer for 5 more minutes.
If you like your soup a little thicker, use the back of a spoon or a fork to crush some of the beans.
Just before serving, stir in the spinach and allow to wilt. Ladle the soup into bowls, garnish with parsley, and serve.