Rinse the carrots, remove the skin and grate. Remove the peel from the onion and dice very finely. Stir the water with the vegetable soup. Melt the butter in a saucepan and sauté the onions until translucent. Add the carrots and sauté them as well. Deglaze with the vegetable soup and gently simmer everything together over low heat until the carrots are soft.
Stir together sour milk and cornstarch and thicken the soup with it. Season with garlic salt, ginger, pepper and juice of one lemon.
Coarsely chop the walnuts and roast them briefly in a frying pan without fat. Rinse the parsley, toss dry and chop. Divide the soup evenly among 4 warmed plates, sprinkle with nuts and parsley and place a dollop of double cream in the center of each.