Make the patty mixture: In a large bowl, combine ground beef, egg, half of the minced onion, garlic, almond flour, 2 teaspoons Worcestershire, Dijon mustard, onion powder, smoked paprika, salt, and pepper. Mix gently with your hands until just combined.
Don’t overwork the meat.
Shape the steaks: Divide the mixture into 4 oval patties about 3/4-inch thick. Press a slight indent in the center of each to help them cook evenly.
Brown the patties: Heat olive oil and 1 tablespoon butter in a large skillet over medium-high heat. Sear the patties 3–4 minutes per side until browned.
Transfer to a plate; they’ll finish cooking in the gravy.
Sauté onions and mushrooms: Reduce heat to medium. Add remaining minced onion and the sliced mushrooms to the skillet. Sauté 4–5 minutes until softened and lightly browned, scraping up any browned bits.
Build the gravy: Stir in beef broth and 1 teaspoon Worcestershire.
Bring to a simmer.
Thicken the sauce: Sprinkle xanthan gum lightly over the surface while whisking. Start with 1/8 teaspoon, simmer 1 minute, then add a little more if needed. Gravy should lightly coat a spoon.
Stir in remaining 1 tablespoon butter for richness. Taste and adjust salt and pepper.
Finish the steaks: Return patties and any juices to the skillet. Spoon gravy over them.
Cover and simmer 5–7 minutes, or until patties reach 160°F (71°C) and gravy is silky.
Serve: Garnish with chopped parsley. Serve with mashed cauliflower, sautéed green beans, or a crisp salad.