Peel and dice the potatoes and onion. Then sweat the vegetables in butter. Add the vegetable stock, bring to the boil and cook covered over medium heat for 20 minutes.
Peel the carrots and grate them into fine sticks, blanch them in boiling water for about 3 minutes. Then quench and drain well.
When the potatoes and onions are cooked through and soft, puree the soup finely, add the whipped cream and bring the soup to the boil again. Add table horseradish, stir and season with salt, pepper, sugar and lemon juice. Now add the carrots to the soup and let them get hot.