Rub the mushrooms with kitchen paper or clean them with a brush and cut them into slices. Wash the thyme. Wash and halve the onion. Roast the slices in a large pot without fat and take them out.
Heat the olive oil in the pot. Fry the mushrooms for about 3 minutes while turning them. Deglaze with water. Add thyme, onion halves and peel of 1 organic lemon. Add porcini mushrooms. Season with salt.
Simmer for about 30 minutes. Pour through a sieve. Depending on the recipe, continue to use or pour immediately into hot-rinsed twist-off glasses. Close the glasses.