Heat 1 tablespoon of unsalted butter on a pan over medium heat. Add 4 ounces of onion in, stir for 5 minutes until they turn translucent. Transfer onion to a big bowl, set aside.
Make the beef patties: Add successively in the onion bowl: ground beef, ground black pepper, 2 teaspoons of Worcestershire sauce, garlic powder, oregano, bread crumbs, thyme, and egg. Whisk together.
In another small bowl, whisk together 1 tablespoon of brown gravy mix and 2 tablespoons of water. Pour the brown gravy mixture into the big bowl of beef mixture, add 1 tablespoon of ketchup, then whisk together until well combined.
Divide the beef mixture into 8 equal parts. Use your hands to form them into balls first, then push against their surface to form 8 patties.
Sear the patties: On the same pan as used for the onion at step 1, heat olive oil over high heat for a minute, then reduce it to medium heat and add the beef patties in. Spend 2 minutes to sear the first side, and 2 minutes for the second side. Remove the patties from heat, set aside.
On the same pan, turn it on high heat (without adding extra oil), add the cremini mushroom in, and reduce the heat to medium-low. Stir fry for 5 minutes.
Add in the following ingredients successively: 4 ounces of onion, 1 tablespoon of butter, garlic, flour, mustard, 2 tablespoons of ketchup, 2 teaspoons of Worcestershire sauce, 1 tablespoon of brown gravy mix (whisked with 1 cup of water). Whisk together.
Add the beef patties back in the pan, reduce the heat to medium-low.
Add the stir-fried cremini mushroom back to the pan, sprinkle parsley on top.
Let it simmer for a minute, then remove from heat.
Serve immediately with pasta (or any veggie of your choice).