Butter a 3 1/2-quart shallow glass baking dish. Arrange the shrimp in the baking dish in a single layer. Cover with plastic and refrigerate.
In a medium saucepan, combine the cream and sherry with the shrimp shells. Add a pinch of salt and bring to a boil. Simmer over moderately low heat for 25 minutes; strain through a coarse sieve set over a large glass measuring cup; you should have about 2 1/2 cups.
Preheat the oven to 400°. Melt the 1 tablespoon of solid butter in a medium skillet. Add the scallions and cook over moderate heat, stirring, for 3 minutes. Add the shrimp cream and simmer until reduced to 2 cups, about 5 minutes. Pour the cream into a bowl and stir in the lemon juice and Worcestershire sauce. Season with salt, pepper and hot sauce; let cool until tepid. Season the shrimp with salt and pepper and evenly pour the cream over them.
Put the oyster crackers in a sturdy resealable plastic bag, press the air out and seal to close. Lay the bag on a work surface and, using a rolling pin or a heavy pan, crush the crackers until coarse crumbs form. Transfer to a medium bowl. Add the 4 tablespoons of melted butter and the paprika and stir to coat.
Scatter the cracker crumbs over the shrimp and pat to smooth. Bake the casserole in the center of the oven for 25 minutes, or until bubbling around the edge and the shrimp are just cooked through. Remove from the oven. Preheat the broiler. Broil the casserole for 30 seconds, rotating as necessary, until the topping is evenly browned. Let stand at room temperature for 5 to 10 minutes before serving.
Make Ahead: The casserole can be prepared through Step 4 and refrigerated overnight. Let stand at room temperature for 20 minutes before proceeding.
Wine Recommendation: A white with bright fruity flavors will stand up to the sherry and spices and complement the creaminess here. Look for the 2002 Santa Julia Torrontes from Argentina or the 2002 Marqués de Cáceres Rioja Blanco from Spain.