Bring a large post of water to a rolling boil, add pasta shells and cook al dente, according to package instructions.
Meanwhile, in a large skillet, add the olive oil and tasso or bacon, cook until just crisp,
then add shallots and garlic. Cook and stir over moderate heat just until shallots are translucent. Add the flour, cook stirring constantly to blend and toast the flour, about 5 minutes. Add the white wine, reduce until almost dry. Add the cream, bring to a simmer until the sauce coats the back of a spoon, about 5 to 10 minutes. Remove from the heat and stir in the cheeses, shrimp and spinach. Gently stir until cheese is melted, spinach is wilted and shrimp is beginning to turn pink. Season with salt and white pepper, to taste. Season with hot sauce, to taste.
Drain the pasta, making sure to shake all of the water off and out of the shells.
In a large flameproof baking dish, place drained shells. Add the cheese and shrimp mixture and gently fold into the pasta. Sprinkle with the bread crumbs and chopped parsley. Place under the broiler until the breadcrumbs are toasted about 2 to 3 minutes.