Combine crabmeat, cracker crumbs, and Parmesan cheese in bowl and mix well. Combine melted butter, Tabasco, and Worcestershire, stir to blend, and add to crab mixture - bit by bit until stuffing is moist and binds together.
Place mushrooms in lightly greased casserole. Divide stuffing evenly among caps. Cover all caps with Mornay Sauce. Bake at 375 degrees F for 20 minutes, top with sliced Gruyere cheese, and continue baking until cheese is melted and golden brown.
Heat milk, salt, pepper, and Tabasco in double boiler. In saucepan, make a roux by combining melted butter and flour. Whisk roux, bit by bit, into milk until the consistency of a loose medium white sauce. Whisk in cheese, bit by bit, and cook 10 minutes, whisking occasionally. Proceed with recipe above.