Place beans in large bowl, cover with cold water, and soak 6 hours, or overnight. Drain, and transfer to medium saucepan with rosemary, salt, (optional parmesan rind) and 4 cups water. Bring beans to a boil. Reduce heat to medium-low, and simmer, partially covered 45 minutes or until beans are tender. Drain, and reserve cooking liquid. Discard rosemary sprig, and set aside. Heat oil and garlic in medium skillet over low heat. As soon as garlic sizzles, remove from heat, and cool. Purée beans, oil, and garlic in food processor until smooth, adding cooking liquid if necessary to make mixture creamy. Set aside.