Adapted from Spend With Pennies
6 ounces sliced cremini mushrooms
One medium yellow onion, sliced
114.5 ounces can low-sodium beef broth
1 ounce package brown gravy mix (dry)
2 tablespoons catsup
1 teaspoon Dijon mustard
2 tablespoons fresh parsley, chopped
1-1/2 pounds ground chuck
1 egg yolk
1/4 cup dried minced onion
1/3 cup Panko crumbs
3 tablespoons whole milk
1 clove garlic minced
1/4 teaspoon Montréal steak seasoning
2 tablespoons cornstarch
4 tablespoons water
Spray slow cooker with Pam, and line bottom with mushrooms and onions.
Combine beef patty ingredients and form into six patties. Place 1-2 Tablespoons of olive oil into a 10" skillet and heat until oil starts to shimmer. Brown patties over medium-high heat about three minutes per side. Remove to a plate lined with paper towels and allow to drain for a moment or two. Place the beef patties on top of the mushrooms and onions in the slow cooker. Combine sauce ingredients, and pour over beef patties. Cook on the low setting for 5 hours.
Remove patties to a warm plate; set aside. Turn slow cooker to high, combine cold water and cornstarch, and stir into the sauce. Allow to cook a few minutes until thickened, and then return beef patties to the sauce. Let heat through, about 5 to 10 additional minutes. Serve over mashed potatoes or alongside rice.