In the midst of winter many people regret not having had the foresight to freeze batches of pesto when fresh basil was in season; others self-indulgently used up their supply much faster than they expected. In either case, here is a recipe that will satisfy pesto addicts anywhere, and can be made in any season.
See all spinach recipes.
Note: This pesto keeps well refrigerated for 2 weeks with a tablespoon of oil poured on the surface to prevent dryness. For freezing, omit the cheese and butter and freeze in an airtight container. Thoroughly defrost before using, and add the cheese and butter after it is defrosted.
Put the spinach, basil, garlic, walnuts, if using, and olive oil into the container of a blender. Blend until smooth, turning off the motor and scraping down the sides as necessary.
Pour the pesto into a container with a tight-fitting lid, and stir in the cheese by hand until blended. Stir in the softened butter and salt by hand until blended.
If the pesto is to be used as a sauce for pasta, add a few tablespoons of the boiling pasta water to the pesto to thin it out before tossing it on the pasta.