Add the butter to a large saucepan or Dutch oven over medium heat. Sauté the onion until translucent. Add the shredded cabbage, grated carrot, and chopped celery. Sauté. Add the bay leaf and black peppercorns. Pour over the water or vegetable stock and bring to a boil. Reduce the heat and simmer, covered, for 15 minutes. Add the peeled and coarsely chopped potatoes to soup and bring back to the boil. Reduce the heat and simmer, covered, until the potatoes are tender, about 10 minutes. Add the chopped fresh tomatoes or undrained canned tomatoes and bring back to a boil. Reduce the heat and simmer, uncovered, for 5 minutes. Season with salt and pepper to taste. Remove the bay leaf and peppercorns from the pot (some cooks leave the peppercorns in). Serve soup topped with fresh dill and sour cream.