Cook mushrooms in a Dutch oven coated with cooking spray over medium-high heat 2 to 3 minutes or until tender. Remove mushrooms; set aside.
Add butter to pan; stir in celery and shallots. Cook over medium heat 5 minutes, stirring frequently. Sprinkle flour evenly over celery mixture; cook 2 to 3 minutes, stirring constantly. Gradually add milk, stirring constantly with a whisk until blended. Stir in basil and next 6 ingredients. Cook over medium heat 3 minutes or until slightly thick. Stir in crabmeat, reserved mushrooms, and sherry. Cook, uncovered, over medium-high heat 5 minutes, stirring constantly. Sprinkle with chopped fresh chives, if desired.