Prepare shrimp and set aside. In a medium heavy saucepan, sauté onion and celery in butter over moderate heat until tender but not browned. Stir in flour and seasonings, blending until smooth. Gradually add milk or milk and half-and-half, blending well. Cook, stirring constantly, over moderate heat until mixture is thickened and bubbly hot. Stir in shrimp and adjust seasoning to taste. Heat through and serve immediately. Garnish each serving with a dollop of sour cream and/or a sprig of parsley or thyme or rosemary. Or, thoroughly chill hot soup in the refrigerator and serve in chilled soup cups; garnish as previously directed.
Note: Cook shrimp in about 6 cups lightly salted boiling water for 3 minutes after water returns to a boil or until shrimp turn a bright coral color. Immediately rinse shrimp in cold water to stop the cooking action. Peel, devein, and remove tails of shrimp. Do not overcook as shrimp will become tough.
Variations: Add seafood seasoning to taste to bisque.
Add a pinch of saffron to bisque.
Reduce milk or milk and half-and-half to 3½ to 3¾ cups total; add ¼ cup or to taste dry sherry or brandy to bisque.