1. Melt butter in a medium-size saucepan; add onion and cook until tender. 2. Blend in flour, 1/2 teaspoon salt and Tabasco sauce. 3. Stir in milk, stirring constantly, until mixture thickens and comes to a boil. 4. Remove from heat; stir in lemon juice, nutmeg and spinach. 5. Peel cooked potatoes; cut into 1/8-inch slices. 6. Place a layer of potatoes in a greased 2-quart casserole; sprinkle with 1/4 teaspoon salt. 7. Sprinkle with half the ham and half the spinahc sauce. 8. Repeat with remaining potatoes, remaining 1/4 teaspoon salt, ham and sauce. 9. Cover and bake in preheated 375"F. oven 45 minutes, or until heated through. NOTE: To bake potatoes: Scrub, dry and prick with a fork. Bake in preheated 425"F. oven 55 to 65 minutes, or until soft. Chill before slicing.