Peel and dice the parsnips, season with salt and sugar and leave to steep. Pour off the resulting liquid and cook the vegetables with the stock (should be just covered) until soft. The broth should evaporate as you do this. Mash the vegetables with a fork or a potato masher.
Stone and finely chop the olives, also finely chop the parsley. Mix both with the vegetables with olive oil. Season to taste with salt, pepper, nutmeg and piment d`Espelette.
Salt and sugar the skrei and fry on the skin in a little olive oil, then fry only briefly on the meat side (the skin should be crispy). Finally season with pepper.
Serving:
Place the vegetables in the middle of a plate and place the fish on top.