In saucepan, melt butter over medium heat. Cook celery, onions, chives, thyme, salt and pepper, covered and stirring occasionally, for about 10 minutes or until softened and translucent.
Pour in stock; bring to boil. Reduce heat and simmer for 10 minutes or until celery is very tender. Add pears; cook for 5 minutes or until pears are tender.
In batches, puree in blender. Return to saucepan; pour in cream and heat through without boiling.