In a medium mixing bowl, combine all ingredients for steak and mix very well (except four and sliced mushrooms and onions).
Place flour into a wide bowl. Separate ground beef mixture into eight even balls. Place the on a sheet of parchment paper. Flatten the balls of meat into patties and lightly coat with flour.
Preheat oil in the large skillet, over medium heat. Place steak patties, sliced mushrooms, and onions into the skillet and cook for about 5 minutes on each side.
Take the patties out and set aside (just the meat patties).
Add butter to the pan and once butter is melted, sprinkle flour over the top. Mix well and slowly pour in beef stock, while stirring.
Add pressed garlic, tomato paste, Worcestershire sauce, thyme, salt and pepper. Mix until all smooth and evenly incorporated.
Bring the meat back into the skillet. Bring mixture to boil and then lower the heat to medium-low. Cover and simmer for about 15 minutes flipping the patties half way through. (You can cut into the thickest patty to make sure it's done.)