In a bowl, combine ground beef, almond flour, egg, Worcestershire, garlic powder, salt, and pepper. Mix gently and shape into 4 oval patties.
Melt 1 tbsp butter in a skillet over medium-high heat. Sear patties 3–4 minutes per side, until browned. Remove and set aside.
Add remaining butter to the skillet, then mushrooms and onion. Cook 6–7 minutes, until softened and browned.
Pour in broth, scraping up browned bits from the pan.
Whisk in xanthan gum a little at a time until the gravy thickens slightly.
Return patties to the skillet, spooning gravy over top. Simmer 8–10 minutes, until patties are cooked through.
Serve hot, smothered in gravy.