Peel the potatoes and cut into cubes. Cut the carrots into slices. Cut the leek into rings. Dice the onion. Sauté the vegetables in melted butter for 5 minutes. Then add the broth, season with thyme, salt, pepper and sugar and bring to the boil. Then cook on a low flame for about 20 minutes. Finally sprinkle the parsley over the stew.
If you don`t like it meatless, you can optionally add 250 g of diced ham and let it stew.