Soak spinach in cold water to cover 1 hour. Drain. Place spinach in a large Dutch oven (do not add water); cover and cook over high heat 5 minutes or until tender. Drain spinach, reserving 2 tablespoons liquid. Chop spinach, and set aside.
Melt butter in a 10-inch skillet over low heat; add flour, stirring until smooth. Add spinach; cook 10 minutes over medium heat, stirring frequently. (If necessary, gradually add reserved liquid for desired consistency.) Spoon spinach mixture into 4 lightly greased 6-ounce custard cups. Set aside.
Fill a saucepan or skillet with 1 1/2 inches salted water, and heat to boiling. When water boils, lower heat to simmer. Break eggs, one at a time, into a clean custard cup. Hold the lip of the cup close to water, and gently slip egg into the water. Simmer until eggs reach desired degree of doneness. (Do not allow water to boil.) Remove eggs with a slotted spoon, and drain well.
Place a poached egg on top of spinach in each custard cup. Cover each with cream sauce; top with cheese, and bake at 400° just until cheese melts. Serve hot.