First, make the filling by warming the oil in a pan and wilting the spinach for just 1-2 minutes. Take off the heat and leave to cool. Don’t skip this step or the heat will make the filling too loose to work with.
When the spinach is cold, press the excess liquid out, then chop roughly and transfer to a bowl..
Add the ricotta, nutmeg, and Parmesan and stir through.
Cover the bowl and put in the fridge to chill while you make the pasta.
Prepare the pasta dough
Start the pasta by adding the flour to a food processor bowl and pulsing the processor as you add the eggs one at a time until fully combined into a slightly sticky crumb.
Turn out onto a clean surface and knead briefly into a smooth dough, then cut into quarters and cover with cling film.
Leave to rest for 10 minutes to make it easier to work with.
Fill the ravioli
Make up a long strip of pasta either rolling by hand or with a pasta machine to about two notches from the thinnest setting (I went to #7).
Dust a surface with polenta and lay the strip out on it.
Spoon the filling in equally quantities (about 1 level tablespoon) along the length of the strip, leaving a little gap between each spoonful.
Take a new piece of pasta dough and create a second strip.
Brush a little water onto the bottom layer of pasta around each blob of filling, then place the second sheet of pasta carefully on top.
Press firmly around each round of filling, pushing out the air and sealing well all the way round.
Cut out each of the ravioli rounds using a large cookie cutter, glass tumbler or knife and, if necessary, press around the edges again to seal.
If piling them up, sprinkle polenta on top of each one or they’ll stick together.
Discard the pasta offcuts and repeat steps 1-7 for the remaining dough and filling – you should end up with 18-20 ravioli in total.
Leave them to firm a little while you make the sauce.
Prepare the sauce
Warm the oilve oil in a pan over a low heat.
Add the onion and garlic to the pan, frying gently for 2-3 minutes until translucent.
Add the passata and stir, then bring up the heat to a gently simmer for 10 minutes until it thickens by a third.
Bring it all together
Drop the ravioli into a large pan of boiling, salted water. They’re ready when they float to the top, which takes just 3-4 minutes.
With a slotted spoon, lift the ravioli onto a plate.
Taste and season the sauce as needed (in Rome, they favour condiment rich sauces, but you can use sparingly if you prefer) then spoon over the ravioli.
Top with a little shredded basil and extra cheese, if desired.