Rub the elk roast with salt and pepper. Roast in a preheated 400-degree F oven for about 25 minutes per pound, or until the thermometer registers 140 degrees. While the elk is roasting, periodically, baste the roast with the rendered duck fat to maintain the moisture. Let roast cook until an inserted meat thermometer reads 155 degrees. Let the roast rest for 10 minutes before slicing and serving.