Ingredients

• 1 (2- to 2 1/4-lb) tri-tip beef roast (also called triangular roast; about 2 inches thick)
• 1 1/2 teaspoons salt
• 1/4 teaspoon black pepper
• 1 tablespoon olive oil
• 1 1/2 lb cherry tomatoes (5 cups)
• 1/2 teaspoon salt
• 1/4 teaspoon dried hot red-pepper flakes
• 1/4 cup plus 2 tablespoons extra-virgin olive oil
• 1 cup firmly packed fresh flat-leaf parsley leaves
• 1 garlic clove, sliced
• 1 tablespoon red-wine vinegar
• Special equipment: a well-seasoned 10-inch cast-iron skillet; an instant-read thermometer

Instructions

1. Put oven racks in upper and lower thirds of oven and preheat oven to 425°F.
2. Pat roast dry and sprinkle with salt and pepper. Heat oil in skillet over moderately high heat until hot but not smoking, then sear roast until underside is browned, about 4 minutes. Turn meat over, then transfer skillet to upper rack of oven and roast until thermometer inserted 2 inches into center of meat registers 120°F, 20 to 25 minutes. Transfer to a cutting board and let stand 15 minutes. (Internal temperature of meat will rise to 130 to 135°F for medium-rare.)
3. Make sauce while meat cooks: Toss together tomatoes, salt, red-pepper flakes, and 1/4 cup oil in a 13- by 9-inch glass baking dish. Roast on lower rack until tomatoes burst and release their juices, about 30 minutes. Meanwhile, pulse parsley and garlic with vinegar and remaining 2 tablespoons oil in a food processor until chopped, then transfer to a bowl. Stir tomatoes with their juices into parsley mixture. Slice roast across the grain and serve with sauce.
4. Toss together tomatoes, salt, red-pepper flakes, and 1/4 cup oil in a 13- by 9-inch glass baking dish. Roast on lower rack until tomatoes burst and release their juices, about 30 minutes.
5. Meanwhile, pulse parsley and garlic with vinegar and remaining 2 tablespoons oil in a food processor until chopped, then transfer to a bowl.
6. Stir tomatoes with their juices into parsley mixture. Slice roast across the grain and serve with sauce.