In a bowl, mix together 1/3 of the can of condensed French onion soup (set the remainder aside for now) with the ground beef, bread crumbs, egg, salt and pepper. Form into 6 patties.
In another bowl, whisk together the remaining 2/3 can of condensed French onion soup with the 1 tbsp of flour until smooth. Then add in the ketchup, water, Worcestershire sauce and mustard powder and stir to combine. Set aside.
In a large skillet over medium high heat, brown the patties on both sides (about 2-3 minutes per side). Remove the patties from the pan and discard any grease, then put them back in the pan and turn heat to low.
Once patties are back in the pan, pour the ketchup/Worcestershire sauce mixture over the patties, cover and cook on low for 20 minutes, stirring occasionally.
Notes
Enjoy with some creamy mashed potatoes to pair with the delicious gravy!