Creamy Potato and Celeriac Mash

1.5 pounds potatoes, peeled and chopped
2 cups whole milk
8 oz celeriac, peeled and chopped
3 tablespoons butter (or more!)
Salt, pepper and nutmeg to taste

Boil potatoes until tender and drain.  Boil celeriac in milk until very soft.  Drain, reserving milk.  Mash each separately until very smooth.  Combine adding milk, butter, seasonings to taste.  Serve hot!