Cut asparagus into 1-2 inch pieces. In skillet, sauté asparagus and onion in 1 Tablespoon of butter until tender/crisp. Transfer to a 1 1/2 qt. baking dish.
In saucepan, melt 2 Tablespoons of butter, add flour and stir until smooth; add milk and cook until thickened and smooth; add cream cheese, salt and pepper. When cream cheese is melted, pour mixture over asparagus and onions.
Sprinkle with shredded cheese. Melt remaining butter and toss with breadcrumbs. Sprinkle over casserole. Bake uncovered at 350 degrees for 45 minutes.