*To make crawfish stock: Boil crawfish peelings with a little dry sherry (or water), garlic, onion juice, celery seed and a dab of butter. Strain. May be frozen for future use.
Preheat oven to 350°F.
Place tails and bread in food processor. Pulsate until coarsely ground. Set aside. Melt butter and add flour, stirring constantly. Add half and half gradually and let mixture simmer until reduced to 1 cup. Add reserved crawfish mixture and seasonings to half and half.
Boil macaroni in salted water until al dente. Stir gently while cooking to keep shells apart. Drain. Cool enough to handle. Stuff each shell with a heaping tablespoon of crawfish mixture, closing shell over filling.
To make sauce: Boil cream, stock, and butter in a medium saucepan until reduced by one-half. Add basil and salt and pepper to taste. Place small amount on bottom of casserole dish or individual ramekins coated with nonstick spray. Place stuffed shells in dish, pouring remaining sauce over the top. Sprinkle with Parmesan and paprika. Cover and bake at 350 degrees for 20 minutes. Remove cover and bake an additional 5 minutes.