Stir together hoisin, ginger, garlic, vinegar, soy sauce, and pepper until well blended. Rub marinade all over roast, coating it well. Place in a glass baking dish, cover, and allow to marinate in the refrigerator at least 8 hours, but preferably overnight.
Remove tri-tip from the refrigerator and let it sit at room temperature for 30 minutes. Heat oven to 375°F. Blot roast dry with paper towels to remove some of the excess marinade.
Heat olive oil in a large frying pan over medium-high heat. Sear roast for about 2 minutes per side or until nicely browned. Transfer roast to a small roasting pan or baking dish and place in the oven. Cook until roast reaches an internal temperature of 125°F for medium rare, about 20 to 22 minutes.
Remove roast from the oven and cover loosely with foil. Let rest for 15 minutes before carving. Slice tri-tip across the grain and serve.
Beverage pairing: Torbreck Woodcutters Shiraz, Australia. The hoisin, ginger, and soy give the beef a sweetness and spiciness that is best matched by a wine that also has both. Australian Shiraz is such a wine, and this one has a plump core of sweet blueberry fruit that is appropriately undercut with pepper and spice.
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