Peel, wash and cut the carrots into small cubes. Bring the stock to the boil, add the peas and simmer for about 5 minutes. Take out about 1/4 of the peas with a skimmer. Peel garlic and press it through the garlic press.
Wash the chervil, dab dry, put something aside for garnishing. Add the garlic and chervil to the soup, puree the soup finely. Add the carrots and simmer for 6-8 minutes, stirring frequently. In the meantime, peel onions and cut into fine rings.
Heat the oil in a coated pan and fry the onion rings until golden brown. Cut the sausages into pieces. Heat sour cream, peas and sausage in the soup. Season with salt and pepper. Just before serving, sprinkle the soup with onion rings and garnish with chervil.