Preheat oven 375 degrees F.
Puree pecans in food processor until mealy in texture. Add the flour and pulse until incorporated with the pecans.
Season the filet mignon with the salt and pepper. Sear the filet in hot vegetable oil until it has a rich brown color, turning to brown all sides. Remove from the pan and let it cool for a few minutes.
Brush the filet with a light coat of Dijon mustard, using a pastry brush. Pack the pecan and flour mixture on the filet and saute in fresh oil until golden brown on all sides.
Place the filet on a rack and finish roasting for approximately 10 minutes. Serve with the Port wine sauce.
Sweat shallots in 2 ounces of the butter. Add the peppercorns, wine and vinegar. Reduce the wine slightly. Add the demi glace and simmer until it develops the right consistency and flavor. Strain and stir in the remaining butter.