- To prepare marinade, place all Secret Sauce ingredients in a medium bowl and mix well. Remove 1/4 cup mixture and set aside in a covered container in the refrigerator.
- Place steak and remaining Secret Sauce in a large resealable bag and seal well; refrigerate for 2 hours (or for up to 24 hours).
- Allow reserved Secret Sauce to come to room temperature. Remove steak from bag and discard bag and marinade. Grill steak over medium heat for 4 to 5 minutes on each side or until meat is cooked to an internal temperature of 145°F for medium, or to your preferred doneness. Remove from grill and place on a large piece of foil; let stand for 5 minutes.
- Transfer to a cutting board and slice thinly against the grain. Drizzle with any accumulated juices and reserved Secret Sauce. Garnish with rosemary, if desired.