First, mix the ground beef with the seasonings and the onions. Then, form the patties or the hamburger steaks. The sizes can and will vary but don't make them so big they take forever to cook all the way through.
Prep the ingredients for the mushroom gravy. Take half the mushrooms and chop them up finely.
In a frying pan on medium high heat add a little oil the cook the hamburger steaks until fully cooked. Then, remove from the pan and set to the side.
Then, toss in the mushrooms and let them sweat and cook down, stir often. You'll see them release all the water and then the pan will become dry. After that lower the heat to medium and add in the butter then the flour. Mix everything together then pour in the beef broth.
Now, crumble the beef bouillon cube over the gravy and add in the thyme. Things will begin to bubble and thicken. At this point you can turn the heat off but don't take the pan from the heat source.
Pour in the heavy cream and mix into the gravy. Then, add the hamburger steaks back into the gravy and baste with the gravy. Allow patties to sit in the gravy on the hot stove as it slowly cools. After about 5 minutes you can serve and enjoy.