For the pasta, place the flour and semolina in a mixing bowl and make a well in the centre. Gradually add the oil and 225ml/8fl oz of water, incorporating the liquid to form a dough. Knead until the dough is smooth and elastic and then form into a ball. Wrap in cling film and leave to chill in the fridge for 1 hour.
Unwrap the dough from the cling film and roll out on a lightly floured work surface (or use a pasta machine) to a thickness of 1mm. Cut 9-cm/3½-in rounds from the dough using a circular cutter. This should make 24 culurgiones.
For the filling, mix the Parmesan, ricotta and egg yolks together in a bowl. Season with salt and pepper. Add a teaspoon of the Parmesan mixture to the centre of each pasta round. Fold the sides up and seal along the top, pinching as you go with your fingers, so it resembles a dumpling shape.
Bring a saucepan of salted water to the boil. Add the stuffed pasta and simmer for 2–4 minutes (or for 2 minutes after they float to the surface of the water). Drain the pasta, retaining some cooking water.
For the Parmesan butter, heat the butter, sage leaves and Parmesan in a small frying pan and add a small amount of pasta cooking water. Stir the butter into the stuffed pasta and serve immediately.