The secret of a successful soup often lies in a well-flavoured stock, so if you haven't the time or inclination to make your own, choose a good-quality commercial one.
You can make your own stock in the slow cooker with leftover bones and vegetables, boiling water and a bouquet garni, left on Low all day.
Take care not to over-season soups - especially if you have used a ready-made stock, as some already have a high salt content.
As you lose so little liquid during cooking, add two-thirds of the liquid when adapting conventional recipes.
You can thicken with cream, milk or egg yolks for the last 30 minutes of cooking time.
If necessary, thin down with boiling water or stock.
Vary the recipes to suit what is in season.