Trim the leeks, rinse them and cut them lengthwise and then into thin slices. Place 2 tablespoons butter in a pan and sautÄ the shallots, then add the white wine. Boil for 3 minutes. Add the mussels and pepper. Cover and cook until the mussels have opened. Remove them from their shells, and keep them in a warm place. Strain the mussel juice through a double thickness of cheesecloth. Pour it into a pan and add the saffron. Heat and reduce by a half. In a frying pan, cook the leeks in olive oil for 3 minutes. Pour in the saffron-wine mixture and simmer for 5 minutes. Add the crÅme fraöche and stir. Off the heat, whisk in some cubes of butter until the sauce is smooth and velvety. Divide the mussels between individual plates, spoon over the sauce. Sprinkle with parsley and serve very hot.
