Butter a 6 cup soufflé dish; dust the bottom and sides with two tablespoons of The bread crumbs. Set aside. In a 4-quart saucepan over medium heat, melt butter. Stir in flour; cook 1 minute.
Whisk in milk; cook stirring with a whisk until mixture boils and thickens. Squeeze spinach dry; stir into sauce with cheese and ham. Cool. Preheat oven to 350 degrees.
Beat the egg whites with the cream of tartar to stiff peaks. Stir yolks into Cheese sauce, then gradually and gently fold in whites just until blended. Pour mixture into prepared soufflé dish. Bake 35 to 40 minutes. Serve immediately.