Add lean ground beef, chopped onion, garlic powder, egg, Dijon mustard, Worcestershire sauce, coconut flour, pepper, and kosher salt to a large bowl.
1 pound lean ground beef, ½ medium onion, 1 teaspoon garlic powder, 1 large egg, 1 teaspoon Dijon mustard, 1 tablespoon Worcestershire sauce, ⅓ teaspoon ground black pepper, ½ teaspoon salt, 1 tablespoon coconut flour
Mix until combined, then form into 4 large oval patties (or 6 smaller patties). If desired, place patties in the refrigerator for about 15-30 minutes after shaping to help them keep their shape as they cook.
Heat oil in a large pan over high heat. Add the hamburger steaks (do not overcrowd the pan - cook in batches if necessary) and cook for 1 minute until browned on one side.
2 tablespoons olive oil
Gently flip the steaks and brown on the other side. Only cook until browned, then remove the patties to a plate and set aside.
If necessary, add additional oil to the pan. Add remaining chopped onion and cook until translucent. Add mushrooms and cook until browned, about 2-3 minutes.
½ medium onion, ½ pound cremini mushrooms
Reduce the heat to medium and add beef broth, Worcestershire sauce, salt, and pepper to the mixture. Slowly mix in heavy cream.
2 cups beef broth, 1 tablespoon Worcestershire sauce, Salt and pepper to taste, ¼ cup heavy cream
Add the hamburger steaks and any juices on the plate to the mixture. Cook about 6 minutes, until the beef is cooked through (the USDA recommends 160°F to 165°F - see our beef temperature chart) and the gravy has thickened somewhat.
Once cooked through, remove the steaks to a plate. Remove 1 cup of liquid from the gravy and mix it with xanthan gum (or cornstarch). Whisk well, then add the mixture back to the gravy and stir until it thickens. Spoon the gravy over the steaks.
½ teaspoon xanthan gum