1. Put garlic, onion, and celery into a food processor and mince finely. Mix into beef along with salt, pepper. Bread crumbs, egg, and parmesan cheese. Mix well. Then form into 5 patties.
2. In a medium sauté pan over medium heat, add about 2 tablespoons olive oil. Add patties to pan and fry on first side until browned. Gently turn over to finish. When the patties are fully cooked. Remove from pan and set aside.
3. In same pan add mushrooms, and sauté until browned and caramelized. Then add beef broth and bring to a simmer. Mix water and cornstarch. Stirring vigorously slowly add the cornstarch and water mixture. Add enough to make gravy consistency. You may have to add more or less depending on the thickness you like.