Cavatelli is a short and twisted pasta, in case it’s hard to find, you can always use casarecce or a penne type of pasta instead.
To prepare the pesto:
Using a pestle and mortar pound about three-quarters of the pistachios along with the garlic to a smooth paste.
Keep on pounding, gradually add the basil leaves and then slowly pour over the olive oil.
Now add the grated pecorino and the rest of the pistachios, and pound again (leaving the pistachios slightly coarse). Season to taste.
Bring a pan of salted water to the boil. Add the pasta and cook until al dente, for about a minute less than the time given on the packet.
Reserve some water from the pan and drain the pasta.
Put the pasta back into the pan, toss with the pesto adding a little bit of cooking water to loosen the sauce slightly.
Serve immediately with some grated pecorino on top.