Preheat oven to 350°F. Lightly grease an 8x10 pan.
Bring a large pot of water to a rolling boil. Rinse the scallops, drop into boiling water, cooking for 2 minutes. Remove with a slotted spoon and pat dry with paper towel. Place in the prepared pan.
In a medium saucepan over low heat, melt the butter and stir in the flour. Whisk in cream, milk, wine and 1/4 cup Parmesan cheese. Season with salt & pepper to taste. Add spinach, garlic, onions, and mushrooms and cook in sauce until softened, about 5 minutes.
Pour the cream sauce over the scallops. Top with 1/2 cup Parmesan and bread crumbs. Sprinkle Old Bay Seasoning over.
Bake in preheated oven for 15 minutes or until browned and bubbly.