Separate lettuce leaves, and wash thoroughly. Tear into bite size pieces. Place lettuce and water to cover in a large Dutch oven; set aside 1 hour. Drain.
Place lettuce, 1 cup water, and salt in a Dutch oven. Bring to a boil. Cover; reduce heat, and simmer 20 minutes. Drain well.
Melt butter in a heavy saucepan over low heat; stir in flour. Cook 1 minute, stirring constantly. Gradually add broth; cook over medium heat, stirring constantly, until thickened and bubbly. Add cream; cook 1 minute, stirring constantly. Stir in lemon juice, salt, and pepper. Pour sauce over cooked lettuce. Sprinkle cheese over top.