01 -
In a large bowl, thoroughly mix ground beef, egg, breadcrumbs, beefy onion soup mix, milk, and Worcestershire sauce until evenly combined using clean hands.
02 -
Divide the mixture into eight even portions and shape each into a patty.
03 -
Place flour on a small plate. Lightly dip both sides of each patty into flour and tap off any excess.
04 -
Heat vegetable oil in a large skillet over medium-high heat. Sear patties in batches, cooking until golden brown on both sides but not fully cooked.
05 -
Spray a 6-quart oval slow cooker with cooking spray. Layer patties inside, stacking as necessary.
06 -
In a bowl, whisk together beef broth, au jus gravy mix, minced garlic, Worcestershire sauce, and Dijon mustard.
07 -
Pour the prepared gravy mixture evenly over the patties in the slow cooker.
08 -
Cook on low for 4 to 5 hours or on high for 3 to 4 hours, until patties reach an internal temperature of at least 165°F (74°C). Longer cooking enhances tenderness; expect patty shrinkage.
09 -
Carefully transfer patties to a plate. Pour gravy into a large skillet and bring to a simmer. In a separate bowl, whisk water with cornstarch to create a slurry. Gradually whisk slurry into simmering gravy until thickened, about 1 to 2 minutes.
10 -
Return patties to the slow cooker if desired and pour thickened gravy over them. Keep warm up to 2 hours. Garnish with fresh parsley before serving. Best served with mashed potatoes, egg noodles, or rice.