Toast the pinenuts very lightly, ie heat the pan well and then toast (fry it dry, without oil) for a few seconds, so that the pine nuts don’t start turning brown but remain fresh with just that hint of fragrance which is going to add flavour to the pesto.
Pinch the leaves off the stems of basil, and discard the stems.
To make Purple Basil Pesto
Place the garlic in the food processor along with the salt and process. Add the basil leaves and run the processor on pulse a couple of times, till the basil is crushed. You want the pesto to be a little coarse, not a smooth puree.
Add the pine nuts and again run the processor, about 30 seconds.
Transfer the mixture into a bowl. Add some of the grated Parmesan, stir it into the basil. Add a little of the olive oil, stir again. Add enough oil to give the mixture an oozy consistency, as Jamie says.
Add salt and pepper to taste. I add the salt pinch by pinch as Im terrified of over-salting the pesto.
Add more of the cheese and oil and stir, till you get the consistency that you like.
Use the Purple Basil Pesto to make pasta or spread on some nice bread for a sandwich, or in wraps or even in quesadillas. Or mix into a soft cheese and sprinkle on salads.
Note: Some recipes for pesto advise not adding the cheese to the pesto if you are going to freeze it and not use it immediately, but to add the cheese later on when ready to use.