Fill a large saucepan with cold water, add garlic and bring to a boil over high heat. Add beans and return to a boil. Reserve 1/2 cup of the cooking liquid, then drain the beans and garlic in a strainer or colander.
Transfer the beans and garlic to a food processor. Add parsley, oil and sage. Process, adding some of the reserved cooking liquid if necessary, to make a thick puree. Season with salt and pepper.
Make Ahead Tip: Cover and refrigerate for up to 2 days.