Phase 1: Prep Work (Dry Brining) - The day before cooking, pat the roast completely dry with paper towels. Generously season all sides with coarse Kosher salt. Place the meat on a wire rack set inside a baking sheet and leave it uncovered in the refrigerator for at least 12 hours, or up to 24 hours.
Remove the roast from the refrigerator at least two hours before cooking to allow it to come to room temperature.
Phase 2: Cooking the Base - Preheat your oven to a low 250°F (120°C). In a small bowl, mash together the softened butter, Dijon mustard, minced garlic, chopped rosemary, thyme, and black pepper to create a thick paste.
Rub the herb butter paste evenly over the top and sides of the roast. Insert an oven-safe meat thermometer into the exact center of the thickest part of the meat.
Place the roast (still on its wire rack and baking sheet) into the oven. Slow-roast until the internal temperature reaches 115°F (46°C) for medium-rare. This usually takes 2 to 2.5 hours.
Phase 3: Finishing Touches - Remove the roast from the oven and loosely tent it with aluminum foil. Let it rest on the counter for 30 to 40 minutes. Meanwhile, increase your oven temperature to 500°F (260°C).
After resting, remove the foil and return the roast to the hot 500°F oven for 10 to 15 minutes, just until the crust is deeply browned and caramelized. Slice against the grain and serve immediately.