Instructions:
- Remove steaks from the fridge 45 minutes before cooking to allow them to come up to room temperature. Pat steaks completely dry with paper towels.
- Season steaks liberally on all sides with salt and pepper.
- Heat the oil in a cast iron skillet over high heat until shimmering, almost smoking. Carefully lay the steaks away from you in the hot pan. Do not move them for 3–4 minutes to establish a dark crust.
- Flip the steaks. Immediately add butter, rosemary sprigs, and the smashed garlic cloves to the pan. Tilt the pan slightly and continuously baste the melted, foaming butter over the steaks for the remaining cooking time (until medium-rare, approximately 130–135°F internal temperature).
- Remove steaks immediately when 5°F below the target temperature and rest on a cutting board, tented loosely with foil, for 10 minutes.
- Drain off all but 1 tablespoon of the rendered fat/butter from the skillet. Return the pan to medium heat.
- Sauté the minced shallot until translucent (about 2 minutes). Add the minced garlic and cook until fragrant (about 30 seconds—do not let it burn!).
- Deglaze: Pour in the white wine, scraping up all the brown bits (fond) stuck to the bottom. Let this reduce by half, simmering vigorously.
- Whisk in the Dijon mustard, then slowly pour in the heavy cream while whisking constantly. Simmer gently until the sauce thickens enough to coat the back of a spoon (about 3–5 minutes). Taste and adjust seasoning.
- Slice the rested steak against the grain or serve whole. Drizzle generously with the warm cream sauce and garnish with fresh parsley.