1. Sift the flour and salt on to a work surface and make a well in the center. Beat 2 of the eggs and the oil together and pour into the well. Using your fingertips, draw the flour into the center, gradually incorporating all the liquid to form a rough, sticky dough. Knead the dough for about 10 minutes, adding more flour as needed, until the dough is smooth and elastic. Wrap in oiled plastic wrap and let stand for 30 minutes.

2. To make the filling, place the spinach in a heavy pan. Cover and cook over medium heat for 2 minutes, shaking occasionally, or until wilted. Drain, pressing out as much water as possible, then chop finely and transfer to a bowl. Add the ricotta, Parmesan, egg, and nutmeg and mix, seasoning with salt and pepper.

3. Cut the pasta in half. Keeping the other portion covered, roll out one portion on a very lightly floured work surface into a rectangle about 1/16 in (1.5mm) thick.

4. Using a teaspoon for each, drop mounds of the filling on the pasta, spacing them 1½ in (4cm) apart. Beat the remaining egg and brush it between the mounds. Roll out the second portion of dough to the same size as the first, and place it over the first rectangle. Use your fingertips to press the pasta between the mounds to seal.

5. Cut squares around the mounds with a pasta wheel or sharp knife. Place on a baking sheet lined with a floured kitchen towel and let stand for 1 hour to dry.

6. Bring a large pot of lightly salted water to a boil. In batches, add the ravioli and cook until floating. Transfer to a large warmed bowl and toss with melted butter. Grind pepper over the ravioli and serve hot.