Lima Bean Purée

Combine 6 cups water, lima beans, garlic, and rosemary sprig in large saucepan. Boil until beans are very soft, about 20 minutes. Drain, reserving cooking liquid. Discard rosemary sprig. Transfer bean mixture to processor. Add butter and puree until smooth, adding some of reserved cooking liquid by tablespoonfuls as needed to moisten. Season to taste with salt and pepper. (Can be prepared 2 hours ahead. Let stand at room temperature. Rewarm over medium heat, stirring occasionally and adding more reserved cooking liquid as needed to moisten.)