Cook asparagus until just tender. Melt fat in heavy saucepan. Stir in flour, salt and mustard. Gradually stir in milk. Cook, stirring constantly until thickened. Add cheese and continue stirring until cheese is melted. Divide asparagus into 6 portions. Place asparagus portions on and parallel to narrow end of each ham slice. Roll as for jelly roll with asparagus in the center of each roll-up. Arrange roll-ups in a baking dish with seam side down. Pour sauce over roll-ups. Bake at 350 degrees until sauce is bubbly, about 20 minutes. Note: I always use fresh asparagus in season. And, I use the microwave to cook the asparagus and heat the roll-ups. Cook the prepared roll-ups on medium for 7 to 10 minutes.