Melt butter in saucepan. Add chopped onions and cook until tender. Add sugar, mustard, worcestershire sauce, ketchup, water, and vinegar. Bring to a boil then remove from heat.
Step2
Slit each hotdog down the center and place each one, slit side up, in a shallow baking pan. Cover with sauce.
Step3
Bake, uncovered, at 350 degrees F for about 20 minutes. Baste frequently.