Bring a large pan of water to a boil ready for the pasta.
Working in a frying pan or medium-sized saucepan, warm the olive oil and butter over a medium heat, then add the onion and fry, stirring, until soft and translucent.
Add the peas and stir until they glisten.
Add salt to the boiling water, stir the pot, then add the pasta and set the timer for a minute less than the recommended pasta cooking time.
Add the cream to the peas and simmer gently.
About 30 seconds before the pasta timer rings, add the grated cheese, lemon zest and some white pepper to the cream and pea mix, then raise the heat slightly and stir constantly, so the sauce bubbles and thickens.
When the timer rings, either use a spider sieve to lift the pasta directly into the sauce, or drain the pasta into a colander (save some of the cooking water), then tip into the pea pan.
Toss everything for about 30 seconds; if the mix seems dry, add a bit of pasta cooking water; if it seems loose, add more grated cheese.
The aim is that the sauce thickens on the surface of the pasta and catches the peas.
Serve immediately.
