Cook the pasta according to the packet instructions for 'al dente' or 'just cooked' (if no instructions for al dente then cook for a little less time than suggested). Drain and rinse in cold water and put into a large bowl. Unless serving hot in which case don't rinse in cold water.
Meanwhile, if not using ready-toasted pine nuts, toast the pine nuts in a dry frying pan on a medium heat. Keep an eye on them, tossing them around until they are lightly brown. Then set aside to cool.
Then make the homemade pesto. Put most of the basil, about half of the toasted pine nuts, the garlic and the olive oil into the bowl of a food processor (a small food processor is perfect). Pulse for a few seconds until well combined.
Pour the pesto over the orzo and mix well. Then add the chopped spinach, the rest of the basil (chopped a little), the rest of the pine nuts, the parmesan and vinegar and combine again. Season with salt and pepper to taste.
Spoon the pasta salad into a serving bowl, then drizzle over a little extra olive oil to serve.
