Cross-hatch the fat on top of the beef. Rub the meat with dry mustard, then salt and pepper it. Place in a roasting pan in oven and roast for 17 minutes per pound, about 1 hour and 25 minutes. The beef is rare when an internal thermometer registers 125 degrees.
Heat the oil in a heavy pan and fry the tomatoes until soft. Grind together the garlic and bread in a mortar and pestle, and add to the tomatoes with the ground almonds. Pour in the white wine, stir and reduce to the consistency of thick gravy. Add the chestnuts. Core and roughly chop the pears, add to the pan and heat through. Serve the sauce with the beef.