COOK potatoes and garlic in large saucepan of boiling water 15 min. or until potatoes are tender. Transfer potatoes and garlic to large bowl with slotted spoon, reserving cooking water in pan. Add broccoli to water in pan. Return water to boil; cook 2 to 3 min. or until broccoli is crisp-tender. Drain.
MASH potatoes. Add cheeses, sour cream and pepper; mix well.
STIR in broccoli.