Cut 1 onion in half. Grate 1 half and slice the other. Slice the other onion too.

In a mixing bowl, combine grated onion, ground beef, egg, mustard, 1/2 tsp. salt, 1/4 tsp. pepper and garlic powder. Make into 4 patties.

Heat oil in a skillet over medium-high heat. Sear patties for 2 minutes on each side. Remove to a paper-towel-lined plate. Pour off fat from skillet.

In the same skillet, saute sliced onions for 10 minutes over medium heat. Add garlic and cook 2 minutes. Pour in broth, 1/2 tsp. salt and 1/4 tsp. pepper.

Bring to a simmer and cook, covered, for 5 minutes. Stir in cornstarch mixture. Add patties and simmer, covered, for 10 minutes.