Mix the gorgonzola with the figs, nuts and sage, season.
Take the meat out of the fridge approx. 30 mins. prior to cooking. Preheat the oven to 80°C, warm the platter and plates. Season the meat, heat the oil in a frying pan. Brown the meat on all sides for approx. 3 mins., set the pan aside. Make an incision approx. 4 cm deep down the length of the meat, stuff with the filling, tie with kitchen twine. Transfer the meat to the warmed platter.
Approx. 1 1/4 hrs. in the centre of a preheated oven. The core temperature should be approx. 55°C. The meat can be kept warm at 60 °C for approx. 30 mins.
Pour the port and stock into the pan, bring to the boil, loosen any bits that have stuck to the pan. Reduce the liquid to half the amount. Bring the reduction to the boil, reduce the heat, then remove the pan from the heat. Add the butter gradually, mixing with a whisk. Return the pan to the hob a few times to barely warm the sauce. Stir until the sauce becomes creamy.
Carve the meat, serve with the sauce.