PLACE potatoes in large saucepan. Add enough water to completely cover potatoes. Bring to boil on medium-high heat. Reduce heat to medium-low; simmer 15 min. or until potatoes are tender. Drain potatoes; return to saucepan.
MASH potatoes until light and fluffy, gradually adding milk alternately with the VELVEETA.
SPRINKLE with the onions.
