The slightly unconventional cooking method here would be familiar to a steak-house chef. The sequence of initial high-heat sear, long rest and oven finish allows the tasty juices to remain in the meat while the heat migrates slowly toward the center in what is known as residual-heat cooking. Once you try this method, it will become part of your repertoire. Creamy white beans are the perfect accompaniment.
Pan-Roasted Porterhouse Steak
1 porterhouse steak, about 1 1/2 lb. and 1 1/4 to 1 1/2 inches thick, patted dry
1 Tbs. olive oil, plus more for serving
Kosher salt and freshly ground pepper, to taste
For the creamy white beans:
2 Tbs. olive oil
1 leek, white portion only, rinsed and finely chopped
1 garlic clove, minced
1 can (15 oz.) cannellini beans, rinsed and drained
1 tsp. fresh lemon juice
1/4 tsp. kosher salt
Freshly ground pepper, to taste
1 Tbs. heavy cream
1 Tbs. coarsely chopped fresh flat-leaf parsley
1 tsp. minced fresh rosemary
Rub both sides of the steak with the 1 Tbs. olive oil. Let stand at room temperature for 1 to 1 1/2 hours.
Heat a large, ovenproof fry pan over high heat until it is very hot, about 3 minutes. Season one side of the steak generously with salt. Add enough olive oil to the pan to coat the bottom and reduce the heat to medium-high. When the oil is shimmering, use tongs to place the steak, salted side down, in the pan, and cook without moving the steak for 2 1/2 minutes. Season the top with salt, turn the steak over and season with pepper. Cook for 2 1/2 minutes more. Transfer the steak to a rack set over a plate, and let stand at room temperature for at least 30 minutes or up to 1 hour.
Meanwhile, make the creamy white beans: In a fry pan over medium-low heat, warm 1 Tbs. of the olive oil. Add the leek and cook, stirring occasionally, until softened, about 5 minutes. Add the garlic, stir once and remove from the heat. In a food processor, combine the beans, the remaining 1 Tbs. olive oil, the lemon juice, salt and a few grinds of pepper and process until smooth. Stir the bean mixture into the leeks and add the cream, parsley and rosemary. Place over medium-low heat until warmed through.
Preheat an oven to 425°F.
Return the steak to the pan, place in the oven and cook until an instant-read thermometer inserted into the steak, away from the bone, registers 130° to 135°F for medium-rare, about 12 minutes, or until done to your liking. Transfer the steak to the rack and let rest, uncovered, for 5 to 8 minutes.
Cut the sirloin away from the bone on one side and the filet section on the other. Cut across the grain into thick slices. Arrange on plates. Serve immediately with the creamy white beans, passing olive oil at the table for drizzling. Serves 2 or 3.