In the bowl of a food processor (or in a blender), add the sage, garlic and pine nuts. Pulse the ingredients a few times until chopped. In a steady stream, slowly add the olive oil while the food processor or blender is running. Stop to scrape down the sides once with a rubber spatula and add the salt and pepper. Run the processor for a few more seconds to combine thoroughly.
Transfer the pesto to an airtight container and store in the refrigerator until ready to use. The pesto will keep in the refrigerator for up to 5 days.