Mushroom soup with buckwheat

Begin by finely chopping the onion and garlic to release their fragrant oils. Carefully slice the mushrooms to ensure even cooking and wash the buckwheat thoroughly under cold water to remove any impurities. Heat the vegetable oil in a saucepan over medium heat, then gently sauté the chopped onions until they turn translucent and fragrant, taking care not to brown them to maintain a delicate sweetness. Add the sliced mushrooms and garlic to the pan, continuing to sauté until the mushrooms soften and release their earthy aroma. Sprinkle in the salt and crumble the vegetable stock cube, stirring well to combine the flavors. Add the washed buckwheat and the bay leaf, then pour in enough water to just cover the ingredients. Bring the mixture to a gentle simmer and cover with a lid, allowing it to cook slowly to tenderize the buckwheat and meld the flavors, approximately 25 minutes. Just before the buckwheat is fully cooked, season with freshly ground black pepper to taste. In a separate bowl, mix the sour cream with flour until smooth to avoid lumps. Temper the sour cream mixture by adding a small ladle of hot soup broth to it, then slowly stir it back into the soup to thicken and enrich the broth. Finally, stir in the chopped fresh parsley and add a dash of white wine vinegar to brighten the overall flavor. Taste and adjust seasoning if necessary. Serve the soup hot, garnished with extra parsley if desired. For an enhanced experience, accompany with hearty bread to soak up the delicious broth.