Mix the ground beef with heavy whipping cream, finely chopped or grated onion, egg, some of the Dijon mustard, Worcestershire sauce, and garlic powder.
Form the meat into patties and pan fry them in a large skillet for 2-3 minutes per side in the oil until they're caramelized. Set them on a plate to keep warm.
Add the butter to the skillet and add the mushrooms. Sautee the mushrooms over medium-high heat for 4-5 minutes or until they are soft and have given off their liquid.
Deglaze the skillet with ½ cup of the beef broth, scraping up all the yummy bits from the bottom of the pan.
Add the browned beef patties and any liquid from the plate, tomato paste, and remainder of the broth to the skillet and simmer on low, covered, for about 10 minutes or until the beef is cooked through to an internal temperature of 165-F.
Remove the patties from the pan and set them on a clean plate. Thicken with ½ tsp of xanthan gum (optional).
Top the patties with the sauce and enjoy!
