Cook asparagus in a large pot of lightly salted boiling water until tender, 5 to 8 minutes. Drain well and set aside.
Scoop yolks out of hard-cooked eggs and transfer to a bowl; mash yolks with a fork.
Mash deviled ham spread, cream, onion, 3/4 teaspoon dry mustard powder, Worcestershire sauce, and 1/2 teaspoon salt into the yolks until thoroughly combined.
Fill cavities in egg halves with the yolk mixture; set deviled eggs aside.
Melt 6 tablespoons of butter in a saucepan over medium heat, and whisk flour into butter until smooth and bubbling.
Whisk in milk, a little at a time, until the sauce is smooth and thickened; reduce heat to low and simmer for 5 minutes.
Whisk in Cheddar cheese, 1/4 teaspoon dry mustard powder, salt to taste, and black pepper; stir sauce until cheese is melted and incorporated.
Spread asparagus into the bottom of a 9x13-inch baking dish.
Arrange the deviled eggs on top of asparagus; pour the cheese sauce evenly over the deviled eggs.
Mix crushed corn flakes with 2 tablespoons melted butter in a bowl; sprinkle over the casserole.
Bake in the preheated oven until the sauce bubbles and the topping is browned, about 20 minutes.
