Melt butter in saucepan over low heat. Add flour and stir until smooth. Do not brown. Add onions and cook until soft.
Add spinach liquid, stir constantly to avoid getting lumps. Cook till smooth and starts to thicken. Keep stirring. Add all seasonings and cheese. Stir until melted, smooth and thick.
Combine in cooked spinach and 1/4 C. of bread crumbs. Mix till combined and thick.
7. Put into casserole dish. Put 1/4 cup bread crumbs on top. Place in preheated 350° oven and cook for 20 minutes.