For compound butter: Combine shallot and 1½ teaspoon bourbon in small bowl. Use a fork to stir in softened butter, 1½ teaspoon parsley, ¼ teaspoon Dijon mustard, and ¼ teaspoon Worcestershire sauce until well combined. Shape butter mixture into a log using plastic wrap. Wrap tightly and refrigerate 30 minutes or until firm.

For marinade: Place steaks in a large resealable plastic bag. Combine soy sauce, brown sugar, remaining 2 tablespoons bourbon, vegetable oil, remaining 1 tablespoon mustard, balsamic vinegar, and remaining 1½ teaspoon Worcestershire sauce. Pour over steaks in bag; close bag. Turn bag to evenly coat steaks with marinade; refrigerate 6 to 8 hours, turning bag occasionally. Remove steaks from marinade; discard marinade. Let stand at room temperature 30 minutes.

Preheat a charcoal or gas grill for indirect cooking over medium-high heat (375°). Cut a thin lengthwise slice off one side of each potato. Place a potato, cut side down, on a cutting board between 2 chopsticks. Slice the potato perpendicular to the chopsticks, making cuts about ⅛-inch apart and stopping just before the chopsticks (about ¾ of the way through the potato). Repeat slicing remaining potatoes. Place potatoes on a microwave-safe plate and microwave on HIGH 3 minutes.

Spray potatoes with nonstick spray. Cut a 16x16-inch sheet of heavy foil. Place potatoes on foil and fold up sides to form a bowl. Top with half of bourbon butter and 1/4 teaspoon kosher salt; set aside. Season steaks with remaining ¼ teaspoon salt and pepper.

Grill potatoes and steaks 12 to 15 minutes or until potatoes are crisp around the edges and steaks reach 130° for medium-rare doneness, turning steaks halfway through. Remove potatoes and steaks from grill. Sprinkle potatoes with Parmesan cheese. Loosely cover potatoes and steaks with foil; let stand 5 minutes.

Top steaks with slices of remaining bourbon butter. Serve with potatoes and garnish with additional parsley, if desired.