Bring vegetable stock to a boil in a large pot.

Add buckwheat groats, diced potato, diced onion, chopped fresh parsley, fresh oregano, and yeast extract to the boiling stock.

Reduce heat to low, cover the pot, and simmer for 30 minutes.

Check the soup halfway through cooking. If the stock level is low, add milk to maintain a desirable consistency.

Once the vegetables and buckwheat are tender, carefully transfer the soup to a blender or use an immersion blender to liquidize until smooth.

Return the liquidized soup to the pot.

Add milk and soy sauce to the soup.

Reheat gently if needed before serving.

Serve hot.