Peel the parsley root, parsnip, and celery root. Leave the carrot and onions unpeeled.

Place the parsley root, parsnip, celery root, carrot, onions, celery, peppercorns, and bay leaf in a large stockpot and pour in the cold water. Bring to a boil over high heat, then reduce the heat and simmer for 25 minutes.

Discard the vegetables from the stock.

Peel and dice the potatoes. Cut the cauliflower into florets. Scrub and grate the carrot. Add the potatoes, cauliflower, and rice to the pot with the stock and season with salt.

In a frying pan over medium heat, melt the butter. Add the carrot and saute briefly, then add to the soup along with the peas.

Simmer the soup over medium-low heat for 10 to 15 minutes, or until the vegetables are tender, adding the parsley and dill during the last two minutes of cooking.

Serve topped with a spoonful of sour cream.