Step 1: Prepare the Steak (The Crucial First Step)
About 30-45 minutes before cooking, remove the steaks from the refrigerator. Place them on a plate and let them come to room temperature. This promotes even cooking. Just before cooking, pat the steaks completely dry on all sides with paper towels. A dry surface is essential for creating the Maillard reaction, which is the chemical process that forms a deep brown, flavorful crust. Season both sides of the steaks generously with coarse sea salt and freshly ground black pepper.

Step 2: Sear the Steaks
Place a large, heavy-bottomed skillet (a 12-inch cast-iron or stainless steel skillet is ideal) over high heat. Add the high-smoke-point oil. When the oil is shimmering and you see faint wisps of smoke, carefully place the seasoned steaks in the pan. You should hear an immediate, loud sizzle. Let the steaks sear, undisturbed, for 3-5 minutes per side, depending on thickness, until a dark, golden-brown crust has formed.

Step 3: The Garlic Butter Baste
Reduce the heat to medium. Add 2 tablespoons of the butter, the sliced garlic, and the thyme or rosemary sprigs to the pan. As the butter melts and foams, tilt the skillet towards you so the butter pools at the bottom. Using a large spoon, continuously scoop the foaming, fragrant butter and pour it over the tops of the steaks. Continue basting for 1-2 minutes. For a perfect medium-rare (130-135°F), this entire cooking process should take about 6-8 minutes total. Use a meat thermometer for guaranteed accuracy.

Step 4: Rest the Steak (Non-Negotiable!)
Transfer the cooked steaks to a cutting board and let them rest for 10 minutes. Do not tent with foil, as this can steam the crust you worked so hard to create. Resting allows the muscle fibers to relax and the juices to redistribute throughout the meat, ensuring a tender, juicy steak.

Step 5: Cook the Mushrooms and Build the Sauce
While the steak rests, use the same skillet with the garlic butter drippings. Do not wipe it out. Place the skillet over medium heat. Add the sliced mushrooms to the pan in a single layer. Let them cook, undisturbed, for 3-4 minutes, until they are browned on one side. Stir and continue to cook until they are tender and golden. Add the remaining 2 tablespoons of butter and the minced shallot. Cook for another 1-2 minutes until the shallot is soft and fragrant.

Step 6: Deglaze and Finish the Pan Sauce
Pour in the white wine or beef broth to deglaze the pan. Use a wooden spoon to scrape up all the delicious browned bits from the bottom of the skillet. Let the liquid simmer and reduce by about half. If using, stir in the heavy cream and let the sauce simmer for another minute until it has slightly thickened. Taste the sauce and season with a pinch of salt and pepper if needed.

Step 7: Slice and Serve
After the steak has rested for 10 minutes, slice it against the grain into 1/2-inch thick strips. Slicing against the grain shortens the muscle fibers, making the steak much more tender to chew. Arrange the sliced steak on a platter or individual plates, spoon the mushroom sauce over the top, and garnish with fresh parsley.