Remove the peel from the potatoes, cut into cubes, soften in salted water. Drain, steam and pass through the liquid softener. Heat the milk with the butter and a little pepper and stir into the potato mixture with a wooden ladle. Mix until the consistency is fluffy.
In the meantime, soften celeriac cubes in salted water and mash with a hand mixer. Mix the mashed celery with the mashed potatoes.
Fold in wasabi powder (alternatively grated horseradish) and the smoked salmon strips. Season to taste.