Chop the onion.

Dice the potatoes, celery, and carrots.

Sauté the onion in butter until softened.

Add the diced potatoes, celery, and carrots to the pot.

Add salt and boiling water or stock.

Cook until the vegetables are tender.

Press the cooked vegetables and liquid through a sieve.

In a separate small bowl, blend flour with a small amount of cream to create a smooth paste.

Add the remaining cream to the flour-cream mixture and stir to combine.

Stir the cream mixture into the soup.

Bring the soup to a gentle boil.

Season the soup to taste with salt and pepper.

Garnish with chopped parsley or dill.

Serve hot with croutons or noodle puffs.