Prep all your ingredients. Salt and pepper your steaks on both sides and then dredge in the seasoned flour (I didn't measure my seasoning. Actually taste the flour and adjust to your taste preference.)
Let your steaks sit in the flour while you heat a large skillet over medium high heat. Once pan is hot add your oil. You want enough oil to cover the pan by about half an inch. When oil just starts to ripple slowly add your steaks. Do them in batches like I did if you need to. Don't over crowd your pan. I fried up 2 at a time. Brown them on both sides and set on paper towels.
Drain excess oil from pan but leave the brown bits from frying. This will add extra flavor to the gravy. Turn heat to medium low and return pan to stove. Add your onions and butter to the pan and cook down until soft and golden. Scrape the brown bits from pan as the onions cook down.
Once the onions are soft and golden add the garlic and mushrooms. Stir and cook for just a minute. Add the tablespoon of flour and cook into the onions for just a few seconds. Slowly mix in your beef stock. You want to make sure the flour doesn't clump. It helps if your stock is at least room temp but it is even better if it's hot. Stir in the fresh thyme. Taste to see if you need to add any salt or pepper.
Bring to a simmer and then add the steak to the gravy. Making sure to coat them well.
Cover and reduce heat to low. Let simmer for about an hour. stir the gravy and flip the steaks about every 15 minutes. If the gravy seems to thick you can add a little more liquid or if it seems to thin let it cook uncovered for a while. The longer you let the steaks simmer in the gravy the more tender they'll become.
I served mine over rice and a side of cooked greens (kale in this case,) and garnished with chopped chives.
