Peel, wash and grate the potatoes. Squeeze out in a fine sieve. Cut the onion into tiny cubes and mix everything with salt and thyme.
Heat a large non-stick frying pan, add clarified butter and place the potato mixture in 4 - 6 small flatbreads in the pan and press flat. Turn after 1 - 2 minutes. Switch back to low heat. After another 1 - 2 minutes, put the lid on and bake the rösti in 5 - 10 minutes, turning them 1 - 2 more times if necessary. At the end, you may want to fry them again without the lid so that they get nice and crispy.