1.Place flour and salt in a food processor. Add eggs; process until mixture begins to come together.
2.Transfer dough to a lightly floured clean surface and dust with a little of the semolina flour. Knead until dough is smooth. Divide dough into four equal portions; enclose in plastic wrap. Set aside to rest for 30 minutes.
3.Set a pasta machine to the widest setting. Roll one portion of the dough through the machine. Fold in half and roll through the machine again. Repeat this process twice more until the dough is smooth. If sticky, you may need to lightly dust with flour as you go. Fold the pasta in half lengthways, then in half again, then in half again once more until you’ve got a square-ish piece of dough, then turn it 90 degrees and roll out. Repeat three times, reducing the setting as you go. You should have a long length of smooth and silky pasta. Cover with a clean, dry tea towel and repeat with remaining dough.
4.Make ricotta filling. Combine the ingredients in a small bowl; season to taste.
5.To make ravioli, put one length of rolled pasta onto a clean surface. Place heaped teaspoons of the ricotta filling at 5cm (2-inch) intervals along one side. Lightly brush water around each section to help the pasta layers stick together. Fold the other side of the pasta over the ricotta to cover, then, using your fingertips, press firmly around each mound of filling. Cut between the rows with a sharp knife or cutting wheel. Put ravioli onto a tray lined with baking paper; place sheets of baking paper between layers of ravioli. Repeat with remaining pasta and filling. Cover with plastic wrap and refrigerate until ready to serve.
6.Make walnut pesto. Process the ingredients until mixture forms a thick sauce; season to taste.
7.Bring a large saucepan of salted water to the boil. Drop in the ravioli and cook for 4 minutes. Remove with a slotted spoon.
8.Divide ravioli between four warmed pasta bowls, drizzle with a little extra virgin olive oil and serve with generous spoonfuls of walnut pesto.
Recipe is not suitable to freeze or microwave.
Pasta flour or 00 flour is a finely milled flour with a high gluten content that creates a strong structure specifically suited to fresh pasta. If unavailable, you can use plain (all-purpose) flour.