SautÄ the onion in the butter without letting it color. Pour in the wine, 10 peppercorns and the bouquet garni and bring to a boil. Add the mussels, cover and when they open remove them from their shells and place on a serving platter above a pan of hot water, so they stay warm. Let the mussel juice stand for a minute, then strain it. In a saucepan melt the rest of the butter, add the flour, and stir. Add the mussel juice and cook until the sauce thickens. Whisk the egg yolks and crÅme fraöche together with the juice of half the lemon. Pour into the sauce, taste for seasoning and add the parsley. When it comes to a boil, pour over the mussels. If you have to wait, keep the mussels covered so they won╒t dry out.
