When the cook time is finished, drain the beans and reserve at least 1 cup of the cooking liquid. Discard the spent rosemary sprigs.
Place the drained beans in a food processor and add the roasted garlic, olive oil, and salt along with 2-3 tablespoons of the cooking liquid.
Pulse the mixture, stopping often to scrape down the sides of the work bowl, then - with the motor running - drizzle in more cooking liquid until the mixture is light and creamy but still thick and spreadable.
Adjust salt to taste, then serve immediately or refrigerate. Serve with pita, cucumbers, crackers, or bread.