Preheat oven to 350 degrees.   Bring a medium pot of water to a boil, add shrimp and boil for 1 - 2 minute or just until they are pink, immediately drain and rinse under cold water, set aside.  Cook spinach according to package directions, drain well, set aside.  Melt butter, add flour and stir with a whisk for one minute.  Slowly add warmed milk and continue cooking over medium heat until the sauce is thick and creamy.  Remove from heat, add salt and pepper, dry sherry and 1/4 cup Parmesan cheese.  Spread spinach in the bottom of a shallow casserole dish.  Top with shrimp.  Cover with the sauce.  Sprinkle with additional Parmesan cheese.  Cover with foil and bake for 20 minutes.  Remove foil and broil until brown and bubbly.  Serve.   

This dish can be made ahead, by layering the spinach and shrimp, refrigerate.  When ready to bake, top with the hot sauce and bake as directed.