Wash the potatoes and boil them in lightly salted water until tender.
Pour off the water and steam away the moisture on the potatoes in the pot. Then mash them lightly with a ladle or spoon.
Gently mix the crab, crème fraiche, butter, salt, pepper and fine-cut chives into the mashed potatoes. Add a few drops of vinegar for taste.
Serve the compote warm with the fried halibut and leek vinaigrette.