Put the pan back over a low heat, then pour the beans into the remaining guanciale fat. Turn up the heat to medium and cook for 3-4 mins until steaming, then remove from the heat and pour in the egg and parmesan mixture gradually, mixing continuously. Mix in the few tablespoons of the bean liquid from the jar to loosen the sauce to a silky consistency. Serve topped with more parmesan and a grinding of black pepper.
