To ground beef add: other half of the garlic/onions,
breadcrumbs, egg, mustard, ketchup, salt, Worcestershire sauce, and pepper. Stir to combine. Form into 7 even sized patties. Cook 3 min per side until cooked through.
In a separate pan, add butter, then, flour: whisk to a roux. Add broth, mustard, Worcestershire, and sugar; whisk to smooth. Bring to a boil. Add onion/garlic & mushrooms, stir.
Season to taste.