1. It's odd that I chose to write this recipe, as the pasta shapes are very small, and with my big fingers, I find them quite difficult to make! (The answer, of course, is to make them bigger, as tortelloni.) Also known as Venus's belly buttons, they are very fiddly, but delicious. The classic way of eating tortellini in Emilia-Romagna, where they hail from, is in brood (in a good broth) as a pasta soup, but they are also good eaten with a simple tomato sauce or with sage, as here.
2. Using a glass or something similar, cut your pasta sheets into little circles about 3-4cm in diameter. Cover with a damp cloth while you make the filling.
3. For the filling, boil the cabbage leaves in lightly salted water until very soft, about 15 minutes. Drain and leave to cool, then chop up roughly. In a blender, or with a hand blender, mince the cabbage, pork and mortadella together very finely, adding some salt, pepper and nutmeg to taste.
4. Put the pasta circles on a work surface. Put a little bit of the filling on one side of a circle, and fold the sides together over the filling to make a half-moon shape. Press to seal, using a little water to help him adhere. Then take the two outside edges and bring them together around your little finger, pressing together to seal. Cook in plenty of lightly salted boiling water for 1 ½ minutes, or until al dente.
5. Meanwhile, melt the butter in a pan, add the sage leaves and sauté for a minute or two. Add the Parmesan, and pour over the tortellini. Serve immediately.