Preheat oven to 400 degrees. Butter a shallow casserole dish. Melt 2 tablespoons butter in large skillet. Saute asparagus 2-3 minutes until barely tender. Remove from pan and set aside.
In same skillet sauté onion in 2 tablespoons butter until onion is soft. Stir in flour, salt and pepper. Cook 1 minute until flour is well blended. Add sour cream and shredded cheese and cook, stirring constantly, over low heat until cheese melts.
Spoon asparagus into prepared casserole. Top with cheese and sour cream mixture. Sprinkle with crumbs and dot with remaining butter.
Bake in preheated oven for 20 minutes. If top is not brown, place under broiler for additional minute or 2. Makes 4-6 servings. Enjoy!