The idea is to get an even cylinder of beef fillet, about 12 inches long and 2 to 3 inches in diameter. Trim the fillet of all fat and sinew, then tie it with a string to keep a round shape. Coat the fillet with freshly ground pepper and salt and refrigerate it for 3 to 4 hours.
Bring to boil in an oval dutch oven: dark beef stock, leeks, carrots, onions, white turnips whole black peppercorns, brandy and ground clove. Simmer gently for 2 hours. Add beef. Cook for about 20 minutes, or until beef is very rare. Remove from liquid, discard any vegetables and let stand for 5 minutes.
While beef is poaching, prepare the sauce. Reduce to about 4 teaspoons: dry white wine, chopped shallots, and whole black peppercorns.
Place in another saucepan: creme fraiche and egg yolk. Whisk together, then slowly whisk in the strained reduction liquid. Cook over gentle heat, stirring until egg yolk thickens the sauce slightly. Add grated nutmeg. Season, to taste.