Saute onion, garlic, leeks, parsnip, celery and peppers in butter about 20 minutes. Add thyme, marjoram, stock and bouquet garni. Bring to boil. Boil for a few minutes. Add potatoes, salt and pepper. Reduce heat and simmer, uncovered for 20 minutes. Stir in tomatoes, simmer until potatoes are tender. Add corn and lemon juice. Cook for 4 minutes. Remove bouquet garni. Adjust seasonings. Let soup stand 15 minutes before serving. Serve sprinkled with parsley, dill and sour cream.