In a large, tall pan, fry the shallots in olive oil for 5 minutes. Add the salts and white wine and cook covered until firm to the bite. Remove the shallots from the pan and set aside.
Pour the water into the liquid in the pan, add the mustard, coriander, nutmeg and tarragon and bring to the boil briefly. Stir in the crème fraîche, heat and season the sauce with salt and pepper.
Put the shallots in the sauce and let them get hot quickly.