Cook spinach and 1 cup water in a saucepan over high heat 4 minutes or until spinach wilts. Drain; rinse with cold water. Drain well, pressing between paper towels. Chop spinach, and set aside.
Melt 2 tablespoons butter in a large skillet over medium heat; add green onions, and saute 2 minutes.
Whisk together eggs, 1 cup half-and-half, 1 teaspoon salt, 1/8 teaspoon pepper, and nutmeg. Stir in spinach, green onions, breadcrumbs, and cheese. Spoon mixture into a greased 9- x 5-inch loafpan. Place loafpan in a baking dish; fill baking dish with 2 inches hot water.
Bake at 350° for 1 hour or until set. Let stand 10 minutes.
Melt remaining butter in skillet over medium heat; add mushrooms, and saute 3 to 4 minutes or until tender. Whisk in flour, wine, and remaining salt and pepper. Cook, whisking constantly, 2 minutes; gradually add remaining half-and-half, stirring until mixture thickens. Serve over Spinach Loaf.