Add pine nuts, Parmesan, garlic, salt, pepper, red-pepper flakes, and olive oil to a blender. Blend on high for 30 seconds. While blender is still running, add basil leaves and continue to blend until finely chopped, about 1 minute longer. Transfer pesto to a small container and cover it with plastic wrap, pressing wrap so it sits directly on pesto.

Cook's Note: The pesto sauce can be made up to 2 days in advance and refrigerated until ready to use.