Wash porcini and soak in 1/4 litre of warm water. In the meantime peel and finely dice the onions. Heat the fat in a pot. Fry the onion in it. Add barley groats. Deglaze with 3/4 litre water.
Add porcini mushrooms with the soaking water. Stir in stock cubes. Cover and cook for about 15 minutes. In the meantime clean and wash the vegetables. Peel carrots. Cut the vegetables into thin slices, add to the stock and cook again for about 10 minutes.
Wash the thyme, pluck the leaves and fold into the soup. Season with salt and pepper and serve. Roasted toast bread tastes good with it.