Cook spinach according to package directions. Drain and reserve cooking liquid.

Preheat oven to 350 degrees.

In a saucepan, melt butter over medium heat. Add flour, stirring until mixture is smooth and blended. Add onion and cook until soft, but not brown.

In a measuring cup, combine milk with enough reserved spinach liquor to make 1 cup liquid. Add liquid slowly to onion-flour mixture, stirring constantly to avoid lumps. Add cream cheese, jalapeno pepper, Worcestershire sauce, celery salt, garlic salt, salt, black pepper, and cayenne pepper. Stir until cheese is melted. Combine with cooked spinach. Place mixture in a casserole dish.

Combine bread crumbs and melted butter. Scatter over spinach mixture.

Bake for 30 to 35 minutes, or until bread crumbs are browned.