In a large bowl, combine the ground beef, bread crumbs, milk, and onion soup mix. Mix until well combined, then shape into 8 patties.

Heat the oil in a skillet over medium-high heat. Lightly coat each patty in flour, then brown both sides until golden (they won't be fully cooked through).

Arrange the browned patties in a slow cooker.

Top with the sliced mushrooms.

In a bowl, whisk together the cream of chicken and mushroom soups and au jus mix. Pour the mixture evenly over the patties.

Cover and cook on Low for 3+ hours, until the beef is cooked through and tender. Top with fresh herbs like rosemary or parlsey as a garnish.