Let the tri-tip roast come to room temperature. Some say to slice off the layer of fat from the roast, but I prefer to leave it on for flavor and to keep the roast juicier.
Preheat the oven to 425 degrees. A hot oven like this will sear the outside of the meat quicker leaving the meat tender and juicy on the inside.
Place the trip tip roast on a roasting pan fitted with a rack. Using a basting brush, liberally coat the top of the roast with Dijon mustard.If you don't have a roasting pan, you can use a baking dish.
Cover the roast with fresh stalks of rosemary and thyme, gently pressing the fresh herbs into the mustard. The sticky mustard helps them stay in place.
Place the meat in the oven and roast for 10 minutes. Turn the heat down to 325 and continue roasting to desired doneness. About 20 minutes longer.
Temp To Cook Tri-Tip: Rare, (120 degrees) medium rare (135 degrees) or medium (140 degrees)
Tent the roast with foil and let is rest for 10 minutes. This will allow the meat to continue to cook while drawing the juices into the meat so they don't spill out all over the cutting board.
To serve, slice thin against the grain.
Optional: I like to make this roast without searing the meat first. I feel the mustard and herb flavors penetrate the meat better placing them on rare beef. If you do want to sear the meat, heat a skillet over medium high heat. Once the skillet is hot, add 1 tablespoon oil. Once the oil is shimmering add the tri-tip roast and sear on both sides. Remove the seared roast to a roasting pan and then slather on the mustard and place the herbs on top. Roast at 425 degrees for about 20 minutes, or to desired doneness. Tip: With its triangular shape, the grain of the meat changes direction. Why against the grain? It shortens the muscle fibers and makes it easier to chew. Be aware of this a follow the pattern of the meat. Look for the direction the grain in running and then cut the meat against this pattern.Presentation tip: Once plated, sprinkle the slices of tri-tip roast with small leaves of fresh thyme. Using delicate thyme leaves rather than fresh rosemary is better because fresh rosemary can be tough and fibery.Substitution for a Tri-Tip Roast: A 2-inch thick or greater sirloin roast or London Broil.