HEAT dressing in large saucepan on medium-high heat. Add leeks; cook and stir 5 min. or until tender. Stir in vegetable blend, broth and water. Bring to boil; simmer on medium heat 10 min. or until vegetables are tender, stirring occasionally.

BLEND, in batches, in blender until smooth. Return to saucepan. Stir in pepper; simmer on low heat until heated through, stirring occasionally.

PLACE crackers in single layer on microwaveable plate; top each with 1 Velveeta slice. Microwave on HIGH 10 to 15 sec. or just until Velveeta is melted. Stir remaing Velveeta into soup; cook until melted, stirring frequently. Serve topped with crackers.