Season the roast generously with salt at least one hour before cooking. Place in the fridge; remove 45 minutes before you’re ready to cook.
Season with pepper. Then, tie the roast with butcher’s twine every 1.5 inches if it’s uneven in shape.
Preheat your oven to 375°F.
In a small bowl, mix the softened butter with garlic, rosemary, thyme, lemon zest, and a pinch of flaky salt. Scoop it onto plastic wrap or parchment, roll into a small log, and refrigerate until firm.
Heat a heavy oven-safe skillet (cast iron works best) over medium-high heat. Add oil and allow to heat for a few minutes. Sear the roast on all sides until browned, about 2 minutes per side. Just before transferring to the oven, brush the top with Dijon mustard.
Transfer the skillet to the oven and roast until the internal temperature hits 125°F for medium-rare, about 20–25 minutes depending on thickness.
Move the roast to a cutting board. While it rests for 10 minutes, slice a pat of your chilled garlic-herb butter and place it on top of the roast. Let it slowly melt on the roast.
Cut the roast into thick slices against the grain and spoon buttery pan juices over the top.
Notes
If you don’t have an oven-safe skillet, place the roast on a wire rack inside a roasting pan after searing it.