Place breadcrumbs in a bowl. Cover with the milk and allow to sit for a few minutes.
Add the beef to a large bowl and add the softened bread crumbs, the egg and the remaining ingredients. Use your hands to gently mix until just combined.
Divide into 4 to 6 balls and form into a thick patty. You don't want them flat like a Smashburger.
Heat oil in a skillet over high heat. Add the patties and cook the first side until browned, then turn and brown the other side (they will not be completely cooked inside but they will finish in the gravy). Remove onto plate.
Add the onion and cook until the onions are a bit translucent.
Add the garlic and mushrooms to the skillet and cook until the mushrooms are browned and they are tender. Don't add the salt until all of the water has released from the mushrooms and has been absorbed or cooked out.
Turn heat down to medium to medium low. Add butter. Once melted, add flour and cook stirring constantly to get the raw flour taste is gone. Maybe a minute or so.
Gradually add in beef broth, stirring as you go. Whisk in remaining Gravy ingredients.
Add steaks along with the juices on the plate. Cook for 5 - 7 minutes, or until gravy is thickened, stirring occasionally around the steaks. If the gravy thickens too quickly, add more water.
Remove steaks onto a plate. Taste gravy and adjust salt and pepper to taste. Serve the steaks topped with the mushroom gravy with mashed potatoes or buttered egg noodles. Enjoy!
