This is ridiculously easy to make, keeps for a week in the fridge, and you don't even need stock. Think about it: stock is just water in which meat, veg and seasonings are simmered. So sausage, celery, garlic and lentils really do transform water into a perfect soup. Chicken or veg stock will intensify the flavor, and leftover bits of ham works well instead of the sausage. This is what I make when I know things are going to get busy and I want to be sure there's something healthy in the fridge to grab for lunch or dinner that counts as a meal all in itself.