Arugula, Steak, and Crispy Potato Salad with Lemony Vinaigrette

Thinly slice 2 shallots. Heat 2 tablespoons oil in a large skillet over medium heat. Add the potatoes and cook, turning occasionally, for 5 minutes. Add the sliced shallots and cook, turning the potatoes occasionally, until they are golden brown and tender, 5 to 6 minutes more. Transfer the vegetables to a plate and cover with foil to keep warm. Heat broiler. Season the steak with 1/2 teaspoon each salt and pepper and place on a broiler-proof baking sheet. Broil to desired doneness, 2 to 3 minutes per side for medium-rare. Transfer to a cutting board and let rest for at least 5 minutes before slicing. While the steak cooks, make the dressing: Finely chop the remaining shallot and place in a medium bowl. Finely grate 2 teaspoons lemon zest into the bowl, then squeeze in 2 tablespoons of juice. Stir in the parsley, capers, garlic, and 1/4 teaspoon each salt and pepper. Gradually whisk in the remaining 4 tablespoon oil. Arrange the arugula, steak, and vegetables on a platter. Drizzle with the dressing.