Melt butter in a Dutch oven over medium heat; add celery and onion, and sauté 5 minutes or until tender. Add crabmeat and next 4 ingredients; cook over medium heat, stirring often, until thoroughly heated.
Stir together cornstarch and 1/4 cup water; stir in 2 tablespoons hot soup. Stir cornstarch mixture and salt into soup; cook 5 to 7 minutes until thickened, stirring often. Top each serving with 1 teaspoon sherry, if desired.