Chop the onion and sauté with the butter in a saucepan. Meanwhile, peel the vegetables and chop them into smaller pieces.
Pour the water into the pan and add the vegetables. Season according to the instructions. Cover and simmer for 35 minutes to allow the vegetables to overcook.
Blend the soup well with a hand blender. Until then, you can make the soup ready for the fridge the day before.
Reheat and stir in the cream. Whisk thoroughly with a hand blender and check the flavours.
Serve the vegetable soups on plates and garnish with fresh herbs or a sprout salad.