In a medium saucepan, melt 2 tablespoons butter, stir in flour, salt and pepper. Gradually add milk. Cook, stirring constantly, until mixture comes to a boil and thickens. Reduce heat and add cheese and cream, stirring over low heat until cheese melts. Mix in cooked chicken or turkey and pour over spinach. Sprinkle top of casserole with bread crumbs. Can be refrigerated at this point. Dot casserole with remaining butter. Bake for 15 minutes then use the broiler to lightly brown the top.