Remove steaks from the refrigerator 30–45 minutes before cooking to approach room temperature. Pat both sides dry with paper towels. Season generously with kosher salt and freshly ground black pepper.

Place a heavy skillet (cast-iron preferred) over medium-high–high heat and let it get very hot (about 4–5 minutes). If grilling, preheat to high.

Add the neutral oil to the hot skillet and swirl. Place the steaks in the pan (do not overcrowd). Sear without moving for 2–3 minutes until a deep brown crust forms. Flip and sear the other side 2–3 minutes.

During the last minute of searing, add 2 tbsp butter, smashed garlic, and thyme. Tilt the pan and spoon the melted butter over the steaks to baste. For thicker steaks (1–1¼"), transfer the skillet to a 400°F (204°C) oven for 3–6 minutes to reach desired doneness; otherwise finish on the stovetop/grill. Use an instant-read thermometer: 130–135°F (54–57°C) for medium-rare.

Remove steaks to a plate or rack and tent loosely with foil. Rest 5–10 minutes while you make the sauce.

Return the skillet to medium heat and remove excess fat, leaving about 1 tablespoon and the fond. Sauté the diced shallot 1–2 minutes until softened. (Add the smashed garlic now if desired.)

Remove the pan from direct heat and carefully add ¼ cup bourbon (stand back if there’s an open flame). Return to heat and reduce the bourbon by half, scraping up the fond.

Add ½ cup beef stock and stir. Whisk in 1 tbsp Dijon mustard, 1–2 tsp Worcestershire sauce, and 1 tbsp brown sugar/maple syrup if using. Simmer until the sauce is glossy and reduced to a saucy consistency (about 3–6 minutes).

Off the heat, swirl in 1 tbsp cold butter to finish and thicken the sauce slightly. Taste and season with salt and pepper.

Slice the rested steaks against the grain, fan on the plate, and spoon the bourbon pan sauce over the slices. Garnish with minced parsley and a light sprinkle of flaky sea salt.