Season both sides of the steak with steak seasoning, salt and pepper. Set aside.
Heat half of the oil on medium heat in a non-stick pan. Sauté the minced garlic and shallot for 2 to 3 minutes. Stir in the Worcestershire sauce, mustard, broth, and cream. Bring to a simmer until the sauce reduces in volume by half and is creamy, smooth and thickened. (the consistency of the sauce should coat the back of a spoon) Season with salt and pepper to taste. Set aside. Reheat right before serving.
Heat the remaining oil in a cast iron or nonstick pan on medium heat. Once hot, sear the steaks on both sides developing a nice char, then add the butter, whole garlic, and rosemary; cook until the desired temperature is reached using a thermometer (see notes below). Once cooked set aside on a cutting board to rest before slicing against the grain.
Serve the sauce with the steak, serve with crusty bread. Garnish with rosemary sprigs.