Layer the ingredients in a 9x13 baking dish:Spread half the asparagus. Top with half the sliced potatoes. Add half the sliced eggs. Sprinkle half the diced ham. Repeat the layers once more.
Melt 4 tablespoons butter in a saucepan over medium-low heat. Whisk in flour and cook for at least one minute. Slowly add milk, stirring constantly until thickened. Add salt, pepper, and dry mustard.Pour sauce evenly over layered ingredients.
Melt remaining 2 tablespoons butter.Mix with crushed Ritz crackers.Sprinkle over casserole.
Bake at 375°F for 20–25 minutes, until heated through and golden brown. Cover loosely with foil if topping browns too quickly.