Slow Cooker Salisbury Steak

For the patties:

1 1/2 lb ground beef
1 egg
1/4 cup minced onion
1/4 cup bread crumbs
1 clove garlic, crushed
1/2 teaspoon salt
1/4 teaspoon pepper

For the gravy:

1 small onion, sliced
6-oz mushrooms, sliced
1 1/2 cup beef broth
1 package of brown gravy mix
1 tablespoon ketchup (optional)
1 tablespoon dijon mustard (optional)
2 tablespoons cornstarch

Directions:

1.	Mix all the patty ingredients together, then form small  patties about 3/4 of an inch thick.
2.	Place patties in the slow cooker, then top with onion and mushrooms.
3.	Mix all other ingredients except the cornstarch and pour over the meat and vegetables. Cook on low for 5 hours.
4.	Remove patties. 
5.	On high setting, whisk in cornstarch and let cook until it thickens.
6.	Add patties back in to coat with sauce before serving.