Salisbury Steak with Mushroom Gravy

INGREDIENTS

1 lb

ground beef

1/4 cup

onion (diced)

egg (beaten)

2 tbsp

ketchup

2 tbsp

dijon mustard ((separated))

2 tbsp

Worcestershire sauce ((separated))

1/3 cup

Panko bread crumbs

1 tsp

kosher salt

1/2 tsp

ground black pepper

2 tbsp

bacon fat or olive oil ((separated))

large onion (sliced thin)

8 oz

mushrooms (sliced)

2 tbsp

flour

2 cups

beef broth

parsley to garnish