In a large bowl, mix together the ground beef, egg, breadcrumbs, onion soup mix, milk, and Worcestershire sauce until well combined. I like to use my (very clean) hands for this.
Divide the mixture into 8 even portions and form them into patties.
Place the flour on a small plate and dip both sides of the patties into the flour, tap off any excess.
In a large skillet over medium-high heat, add the oil. Once hot, sear the patties in batches until golden brown, do not cook the patties all the way through.
Spray a 6-quart or similar-sized slow cooker with cooking spray. Layer the patties into the slow cooker, you will have to stack them.
In a large bowl, whisk together the beef broth, au jus gravy mix, garlic, Worcestershire sauce, and dijon mustard. Pour this mixture over the patties.
Pour this mixture over the patties.
Slow cook on low for 4-5 hours or high 3-4 hours until the patties reach an internal temperature of at least 165°F. The longer the patties cook, the more tender they will become. The patties will shrink a lot during cooking.
Place the patties onto a plate.
Place the gravy into a large skillet and bring to a simmer.
In a small bowl, whisk together the water and cornstarch. Slowly stream in the cornstarch slurry while constantly whisking into the simmering gravy. Simmer until thickened, 1-2 minutes.
You can now serve the patties immediately or place them back into the slow cooker and pour the thickened gravy on top.
Keep on the warm setting. Serve with mashed potatoes, egg noodles or rice.
Video
Notes
Please refer to my FAQ’s and ingredient list above for other substitutions or for the answers to the most common questions.
Regular onion soup mix can be used if you can't find the beefy onion soup mix.
Only lean ground beef should be used to help reduce the amount of grease produced.
A 6-quart oval slow cooker was used here.
These patties can be made larger if you prefer. It will obviously just make less of them.
If you are sensitive to salt, I would suggest use low/no sodium ingredients where possible.