Heat butter and oil in a large nonstick skillet over medium-high heat.
Add celery, shallots, and carrot; saut 3 minutes or until lightly browned. Spoon vegetable mixture into a medium bowl.
Coat pan with cooking spray.
Add button mushrooms; saut 3 minutes or until lightly browned.
Add button mushrooms to vegetable mixture. Coat pan with cooking spray.
Add shiitake mushrooms; saut 3 minutes or until lightly browned.
Add shiitake mushrooms to vegetable mixture.
Combine vegetable mixture and broth in a medium saucepan; bring to a boil over medium heat. Cover, reduce heat, and simmer 30 minutes. Stir in sherry and remaining ingredients. Simmer, uncovered, 5 minutes.