Peel the potatoes and the parsley root and cut them into small cubes.
Cut the onion into small pieces.
Cook the potatoes.
Melt some butter in a pan, and stew the parsley root cubes and the onion for about 10 minutes, until tender. If necessary add some water against burning.
Season the carrot parsley up to taste. I used sage, thyme, nutmeg (a lot), pepper and salt.
When both are tender, add the potatoes to the parsley root cubes and mash them. Add an egg and a dash of cream.