russet potatoes (about 3), scrubbed and sliced into 1/8- inch-thick rounds
kosher salt and black pepper
6-ounce sirloin steaks, about 1 inch thick
white wine vinegar
chopped fresh tarragon
fresh spinach leaves
- Heat oven to 400° F. In a medium bowl, toss the potatoes with 2 tablespoons of the oil, ¾ teaspoon salt, and ¼ teaspoon pepper.
- Transfer the potatoes to a rimmed baking sheet and roast, stirring once, until golden, about 25 minutes.
- Meanwhile, season the steaks with ¾ teaspoon salt and ¼ teaspoon pepper. Heat 1 tablespoon oil in a large skillet over medium heat. Cook to desired doneness, about 4 minutes per side for medium-rare.
- Transfer the steaks to a cutting board, cover with foil, and let stand for 5 minutes.
- Meanwhile, whisk together the mustard, vinegar, and ¼ teaspoon each salt and pepper. Whisking constantly, slowly add the tarragon and remaining oil.
- Toss the spinach with the vinaigrette, slice the steaks, and serve the salad and meat with the potatoes.