Add the butter to a large Dutch oven or other heavy-duty pot over medium heat. When the butter has melted, add the onion and sauté until translucent. Add the cabbage, carrot, and celery. Sauté until the vegetables begin to soften, stirring frequently, about 3 minutes. Add the bay leaf and vegetable stock and bring to a boil over high heat. Reduce the heat to low and simmer, covered, until the vegetables are crisp-tender, about 15 minutes. Add the potatoes and bring it back to a boil over high heat. Reduce the heat to low and simmer, covered, until the potatoes are tender, about 10 minutes. Add the tomatoes (or undrained canned tomatoes) and bring the soup back to a boil over high heat. Reduce the heat to low and simmer, uncovered, for 5 minutes. Season to taste with salt and pepper. emove and discard the bay leaf from the pot. Serve topped with fresh sour cream and fresh dill.