Remove stems from spinach; wash leaves thoroughly in lukewarm water. Place in a Dutch oven (do not add water). Cook over high heat 3 to 5 minutes. Drain spinach well; chop.
Divide spinach evenly into eight 10-ounce custard cups. Carefully break 1 egg on top of spinach in each cup. Sprinkle each with salt; set aside.
Combine milk and cheese in top of a double boiler. Cook over boiling water, stirring occasionally, until cheese melts. Pour cheese sauce over eggs; top with buttered breadcrumbs.
Place custard cups in two 13- x 9- x 2-inch baking pans, and pour hot water into pans to a depth of 1/2 inch. Bake at 350° for 25 minutes
Place custard cups on a baking sheet. Pipe mashed potatoes around edges of custard cups. Broil 6 inches from heating element 2 minutes or until potatoes are browned. Serve immediately.