With a sharp knife, slice 1/2 in. off the top of the onions; peel onions. Cut each into 16 wedges to within 1/2 in. of root end.
Place each onion on a double thickness of heavy-duty foil (about 12 in. square). Fold foil around onions and seal tightly. Place in an ungreased 11-in. x 7-in. baking dish. Bake, uncovered, at 425° for 20 minutes.
In a small bowl, combine butter and mustard. Open foil; fold foil around onions. Brush butter mixture over onions; sprinkle with bread crumbs, salt and pepper.
Bake 18-22 minutes longer or until crisp-tender. Meanwhile, in a small bowl, combine sauce ingredients. Serve with onions. Yield: 8 servings.