Coarse or kosher and freshly ground pepperto taste
⅔cupfinely grated Parmesan cheese
Place the garlic, scallions, parsley and spinach in a food processor or blender and pulse until everything is roughly chopped (or use a mortar and pestle). Add the pine nuts, if using, the oil, and salt and pepper and process, scraping down the sides, part way through, until everything is well blended.
At this point, for best texture you should transfer the pesto to a small bowl or container before stirring in the Parmesan, but you are welcome to throw the cheese into the food processor and pulse to blend.