Making the Patties:
- Spray the crock pot with non-stick spray.
- Crush 4 ounces of saltine crackers, approximately one full tube of crackers. A food processor makes short work of crushing them, or you can place the crackers into a Ziploc bag and use a rolling pin.
- Using a large mixing bowl, add the hamburger, crushed crackers, eggs, ketchup, Worchestershire sauce, garlic, Kosher salt, and fresh ground pepper. Mix the ingredients by hand until the ingredients are just combined. Overmixing can lead to overly dense patties that can get tough.
- Measure 8 ounces for each Salisbury Steak patty (you can adjust the size of your patties to your size preference). Form patties by hand or using a burger press into roughly 5 inch patties. Set the patties aside.
- Using a very hot cast iron skillet, sear the patties for 2 minutes per side. Set the seared patties aside.
Making the Gravy:
- In a medium sized mixing bowl, add the Cream of Mushroom soup, the Beef Consommé, the Lipton Soup mix, and the Aus Jus mix. Using a whisk, stir until evenly combined and smooth. Taste the sauce, season with salt and pepper to your taste.
Preparing the Slow Cooker:
- Arrange the onion slices in a single layer on the bottom of the crock pot.
- Place the beef patties on top of the onions.
- Spread the mushrooms evenly over the patties.
- Pour the sauce over the mushrooms.
- Cook, covered, on high for 4 hours or low for 6 hours.
- Serve over mashed potatoes, rice, or egg noodles.