Janie, here's Nigella's rocket pesto recipe:

50g rocket leaves
2 cloves of garlic, peeled
30g pine nuts
3 anchovy fillets
25g freshly grated parmesan or pecorino
100 ml extra virgin olive oil
1 tbsp ricotta (I have made it without this and it still works - the flavour is more intense)

put everything into the food processor except the ricotta and the olive oil. Blitz to a rough puree, and then, with the motor still running, drizzle the oil down the funnel into the puree until you have, as she says, "a felty green emulsion". stir it all together, add the ricotta and give it one more blitz. Stir through hot pasta.

I have also made this with an olive oil that's been infused with lemon oil, which worked really well (you could add some lemon zest as an alternative).