Preheat the oven to 350 degrees F (175 degrees C).
Season short ribs with salt, pepper, and cayenne. Heat oil in a pan over high heat. Add short ribs and sear until well browned, 3 to 5 minutes per side. Transfer beef to a baking dish.
Reduce heat to medium-high and add onion and mushrooms to the pan. Season with salt. Saute until mushrooms are golden brown, about 5 minutes.
Meanwhile, combine kosher salt, garlic powder, onion powder, pepper, dill, rosemary, thyme, and Parmesan cheese in a small bowl. Sprinkle seasoning mixture evenly over the beef.
Sprinkle flour over the onion and mushrooms. Stir to coat and cook for 2 minutes. Pour in chicken broth, soy sauce, and Worcestershire sauce. Stir and bring to a boil; remove from heat. Pour mixture over the beef and cover with pepperoncini. Place butter on top. Cover baking dish with foil.
Bake in the preheated oven until meat is fork-tender and falls apart easily, about 2 1/2 hours.
Spoon sauce from the bottom of the pan onto the beef to serve. Skim off excess fat as desired.
