Chop the onion and garlic, slice the mushrooms and wash the buckwheat. Heat the oil and lightly sauté the onion. Add the mushrooms and the garlic and continue to sauté. Add the salt, vegetable seasoning, buckwheat and the bay leaf and cover with water. Simmer gently and just before it is completely cooked, add pepper, sour cream mixed with flour, the chopped parsley and vinegar to taste.