Peel the potatoes, carrot and celery and cut into 5 cm cubes. Quarter the leek lengthways, wash and clean, cut the quarters into pieces approx. 1 cm wide. Peel and dice the onions. Melt the butter in a saucepan, sauté the onions over a medium heat until golden. Then add the vegetables (except for the potatoes) and stir-fry until everything starts to brown very slightly. Deglaze the vegetables with the white wine. Add the stock and potatoes, season with salt, pepper, nutmeg and tarragon and cover and cook for 20-25 minutes.