Blend the ricotta with the parmesan, salt, pepper, and two spoonfulls of balsamic vinegar of Modena. Spread the mixture over the mortadella slices and roll. Wrap in aluminum foil and leave to rest in the refrigerator for 2 hours. Slice the mortadella roll into 3-4 cm (1 – 1.5 inch) sections. Serve on a serving dish, drizzling with the remaining balsamic vinegar of Modena.