Preheat the oven to 200°C. Peel and finely chop the onion. Place the ground beef in a bowl and mix with onion, grated boiled potato, egg, mustard, thyme, salt, and pepper. Shape the mixture into an elongated loaf and place it in a greased small baking pan. Bake in the middle of the oven for about 25 minutes. If you want sauerkraut, add it around the loaf when there are about 10 minutes left of the cooking time.
Sauce: Peel and finely chop the onion. Sauté the onion in butter for about 1 minute. Add water, bouillon cube, and crème fraîche. Let it simmer for about 5 minutes without a lid, until the sauce has thickened slightly.
Serve the meatloaf with sauce and lingonberry jam