Heat oil in large saucepan over medium-high heat until hot.
Add celery, potatoes, onion and garlic; cook and stir about 5 minutes or until celery is crisp-tender.
Add broth; bring to a boil.
Reduce heat and simmer, uncovered, about 10 minutes or until potatoes are fork-tender.
Place half the soup mixture in food processor or blender; process until smooth.
Pour into remaining soup mixture.
Stir in milk and mustard; heat 1 to 2 minutes until hot.
Sprinkle with cheese just before serving.