1. To make the patties, combine all ingredients except the butter and mix well by hand, then form into six oblong patties.
2. Melt the tablespoon of butter in a skillet over medium-high heat. Once the butter is melted and hot, add the patties and cook for 2 minutes per side to sear. Remove to a plate.
3. Using the same skillet, melt 2 tablespoons of butter and add the mushrooms and onions. Season lightly with salt and cook, stirring as needed, until both are golden brown, 5-7 minutes.
4. Add the garlic and cook for about a minute, stirring to combine and to prevent burning. Add the beef broth and Worcestershire sauce and bring to a boil. Once the mixture comes to a boil, reduce heat to low and whisk in the heavy whipping cream, stirring for 1 minute to deglaze the pan.
5. Place patties back in the pan and simmer for about 10 minutes to finish cooking. Once the patties are at temperature (160° F) remove to the plate again.
6. With the skillet still at a simmer, sprinkle the xanthan gum over the gravy, whisking as you go. Continue whisking until xanthan gum is fully incorporated and no lumps remain, 1-2 minutes. Season with salt and pepper to taste.
7. Return the patties to skillet, spoon the sauce over the patties, remove from heat, and serve.
Recommended Beer Style: Porter