1. Bring potatoes, rosemary sprig and enough cold water to cover by 2 inches to boil in large saucepan. Reduce heat and simmer 18 to 20 minutes, until potatoes are fork-tender.
2. Drain potatoes; discard rosemary. Microwave milk and broth in microwave-proof cup until hot, 1 minute. Return potatoes to saucepan and cook 2 minutes over low heat to dry. Coarsely mash potatoes with potato masher or large wooden spoon. Stir in broth mixture, salt and pepper until well combined and heated through.