Rolled rib with mushroom stuffing

Sauté the onion and mushrooms in a little oil until the onions are soft and the mushrooms pale brown. Remove from the pan and cool. Mix with the remaining ingredients and season well with freshly ground black pepper (do not add any salt as the anchovies are very salty).
Preheat the oven to 160 ºC (325 ºF). Place the meat, fatty side down, on a wooden chopping board. Season the meat to taste with salt and freshly ground black pepper. Spoon the filling on the meat and roll the meat up lengthwise, securing the roll with string at 1 cm intervals. Place the roll in the rack of an oven roasting pan and roast for 20-25 minutes per 500 g plus 20 minutes extra for medium-done, or 25-30 minutes per 500 g plus 25 minutes extra for well-done. Leave the meat in the warming drawer for about 10 minutes before carving. Use the pan juices to make a tasty gravy. Serve with roast potatoes and vegetables.
Serves 6.