1. Combine sirloin, egg, panko, Worcestershire, salt and spices, mix evenly. Divide into 6 equal portions, and press into 1/2 inch patties.
2. Melt 1 TBSP butter in large skillet over medium heat, add patties and cook 5 minutes per side. Move to holding plate, cover with foil.
3. While patties cook, chop onion and thinly slice mushrooms.
4. Add remaining butter to the pan, once melted, sauté onions for 3 minutes. Stir in mushrooms and thyme and cook 5 minutes.
5. Stir in flour. Cook and stir for 1-2 minutes to lightly brown. Stir in beef broth and sherry. Simmer and thicken 5-7 minutes. Once gravy is thickened, place patties back in to re-warm.
6. Serve warm with gravy over top.