List of ingredients:
450 gram (1 pound/4 cups) black salsify
20 gram (1 1/2 Tbsp.) butter for cooking
20 gram butter (1 1/2 Tbsp.) and 20 gram (2 1/2 Tbsp.) flour for the beurre manié
1/4 litre (1 cup) of the liquid in which the black salsify was cooked (without the butter)
grated nutmeg to taste
pinch of salt
optional pinch of freshly ground white pepper
1 Tbsp. chopped parsley

Preparation in advance:
Clean the black salsify. Sounds simple, but actually doing it takes some work. Some suggest scraping the root like a carrot, others use a peeling knife. I prefer a combination of the two: after rinsing the roots under warm water from the tap, I first use a peeler. Then I scrape any remaing skin off. Then cut the root at once in the desired length, and plunge in cold water.
Knead butter (at room temperature) and flour to a paste.

Preparation:
Boil the black salsify in clean water with a lump of butter for fifteen to twenty minutes. Because the melting butter will form a layer of fat on the water, the black salsify will not be touched by air during boiling, keeping them white.
Drain the vegetables, but catch the cooking liquid.
Take a quarter litre of the cooking liquid, bring to the boil in a small saucepan. add small lumps of the beurre manié whilst beating with a whisk. Heat through for five more minutes on a slow fire, then finish it off with salt, pepper, nutmeg and parsley. Return the vegatbles to the saucepan to heat them again.

To serve:
At once. I prefer boiled potatoes with this, and, bcause it is winter, some black pudding with fried apples

Enjoy!