Sift together the flour and salt into a large bowl and make a well in the centre; pour the eggs and oil into the well then, using either your fingers or a fork, gradually incorporate the flour into the liquid
Knead the dough on a lightly floured work surface until it is completely smooth; wrap in clingfilm and leave to rest for 30 minutes before rolling out; resting makes the dough more elastic
Place the onion in a food processor and process until chopped; add the chicken, spinach and prosciutto and pulse until chopped and blended; transfer to a bowl, stir in 2 tablespoons of the pecorino cheese, the nutmeg and 1 of the eggs; season to taste with salt and pepper
Divide the pasta dough in 4 and roll out very thinly; stamp out 72 rounds with a 7.5cm cutter; brush 36 of the rounds with the other beaten egg and place a generous teaspoon of the filling in the centre of each one; top with another round and press the edges down firmly, pushing out any air bubbles; place on a floured tea towel and leave to stand for 1 hour
Bring a large saucepan of lightly salted water to the boil; add the ravioli in batches and cook for 5 minutes; remove with a slotted spoon, drain and transfer to a warmed dish
Pour the cream into a frying pan, add the garlic and bring to the boil; simmer for 1 minute, then add the mushrooms and 2 tablespoons of the remaining cheese; season and simmer for 3 minutes; stir in the basil, then pour the sauce over the ravioli; sprinkle with the remaining cheese, garnish with basil and serve
4 servings