In a bowl, add the ground beef, breadcrumbs, egg, salt, black pepper, garlic powder, Worcestershire sauce, then mix everything together until evenly combined. Cover and let it set while you prep the other ingredients.
Slice the onions, I suggest on the thinner side for quicker cooking. Measure out the flour and prep the rest of the ingredients so they are in hands reach before you start cooking.
Turn on a pan on medium high heat with about 1 tablespoon of oil. Uncover the bowl with the ground beef and form the patties. Once the pan and oil are hot, add in about 3-4 patties depending on the size. Do not crowd the pan. Just sear the patties on both sides so they have some color on them. You're not trying to cook them all the way through; you want color which adds flavor. Once you've seared all the patties, turn the heat to medium and add in all of the sliced onions.
This part will take the longest. Occasionally, turn the onion over, and stir them into the pan until they are cooked down and caramelized some, not completely. This may take 15 minutes on medium heat.
Once the onions are slightly caramelized, add in the butter. Once the butter has melted, add in the flour then stir everything together with the onions. Next, pour in the beef broth, onion soup mix, and the 2 sprigs of thyme.
Allow the gravy to come to a slight boil. At this step, you want to carefully add back in the seared hamburger steaks. You can crowd them now, remove onions if you need more space by putting them on top of the hamburgers so they continue to cook. Turn the stove to low and allow the hamburger steak to finish cooking slowly in the French onion gravy.
This will take about 10-15 minutes depending on the size of the patties. Once they are finished, the gravy will have thickened on it's own. Now, place the slices of provolone cheese across the top then cover the pan with a lid. This will quickly melt the cheese and once it's melted, you can turn the stove off and begin serving.