Boil the bones in cold water with salt and skim off the foam a few times. In the meantime, prepare the vegetables – wash, peel and cut into cubes or grate them on a large grater. In a saucepan, put two tablespoons of oil and sauté the vegetables (without the onion and pepper) for a few minutes on a low flame, then pour in the bone broth, add the onion and pepper, add the thyme and let the liquid simmer covered for 30 minutes.

In the meantime, prepare the meatballs: sauté the onion in oil, add the rice, leave for a minute, then, after it cools, mix well with the minced meat, then with the rest of the ingredients. After the mixture is homogenized, form balls of the right size (they will swell further when cooked).

Remove the bones from the soup, top up the liquid with a liter of hot water, place the porcini mushrooms one by one in the slowly simmering broth and add the broth. Let the soup simmer for 15 minutes, and before the end, thicken with sour cream mixed with the egg yolk. Season to taste and serve with finely chopped fresh herbs.