Place the basil leaves and pistachio nuts into the bowl of afood processor and pulse a several times.Add the garlic and Parmesan cheese and pulse several timesmore. Scrape down the sides of the food processor with a rubber spatula.While the food processor is running, slowly add the oliveoil in a steady stream. Adding the olive oil slowly, while the processor isrunning, will help it emulsify and help keep the olive oil from separating. Stir in salt andfreshly ground black pepper, add more to taste.