Shape ground beef into 4 patties about 1/2 inch thick.
Cook patties in a large skillet over medium heat 5 to 7 minutes on each side or until desired degree of doneness; drain.
Saute vegetables in butter until tender, stirring occasionally.
Stir in consomme and mustard; bring to a boil.
Reduce heat to low; simmer, uncovered, 20 minutes, stirring occasionally.
Place hamburger patties on French bread; serve with mustard sauce.