Preheat the oven to 250 degrees.
Combine the mustard, olive oil, minced garlic, and thyme leaves together into a paste. Rub all over the roast evenly. Season all sides of the roast with sea salt and freshly cracked pepper, to taste.
Place the meat thermometer into the thickest part of the roast. Place the Dutch oven into the preheated oven and cook until the thermometer reads 115 degrees, about 60-75 minutes (depending on your roast size). Crank the heat up to 500 degrees and continue cooking until the roast reaches 125-130 degrees, for medium rare. Remove from the oven and let the roast rest on a cutting board for at least 10 minutes before slicing and serving. Enjoy.