Start by mixing all your Cajun seasoning ingredients in a bowl. This blend of spices will bring that signature smoky and spicy flavor to the steak. Generously rub the seasoning all over the steak, ensuring every part is coated. Cover the seasoned steaks and place them in the refrigerator for at least 30 minutes or up to an hour to allow the flavors to settle on the meat.

While the steak is resting, combine the marinade ingredients in a large mixing bowl. Whisk together the brown sugar, bourbon, minced garlic, olive oil, mustard, soy sauce, red pepper flakes, thyme, and a pinch of the Cajun seasoning. Keep half of the marinade aside for making the sauce later.

Place your steaks into the marinade, ensuring they are fully submerged. Cover the bowl with plastic wrap and refrigerate for at least 30 minutes. For the best flavor, marinate the steaks for up to 6 hours.

Heat your cast-iron skillet over high heat. Once heated, remove the steak from the marinade and season it lightly with kosher salt and black pepper. Sear the steak in the skillet for about 3-4 minutes on each side for medium-rare, or until the internal temperature reaches 135°F. Adjust the cooking time based on how you like your steak.

Once cooked, remove the steak from the skillet and allow it to rest. This resting period keeps the juices locked in, making your steak even more flavorful.

Take the reserved marinade and transfer it to a small saucepan. Bring it to a rapid boil to kill any bacteria from the raw meat. Then reduce the heat to medium-low and simmer it until the sauce begins to thicken. Whisk in the butter until it melts and integrates seamlessly into the sauce.

Slice the steaks into even portions and place them on a serving plate. Drizzle the bourbon butter sauce generously over the steak, and then garnish with parsley for a fresh pop of color and flavor.