When you’re the daughter of an Iron Chef, you don’t grow up eating typical kids meals. Thanks to her mom, Alex Guarnaschelli, Ava Clark has been learning to cook and understand food since she was a toddler, and now, at 12, she’s searing pork chops, roasting whole fish and steaming artichokes on her own. Her obsession with cooking started at age 3 when she saw her mom making spaghetti and meatballs. “I was like, what the heck is that?” Ava says. Soon she learned how to scramble eggs and slice an avocado, and now she makes dinner a couple of nights a week. “Since I started my first year of middle school, I’ve been going to different grocery stores in the afternoon to check out all the ingredients,” she says. This steak au poivre was inspired by her grandfather, and the potatoes are a favorite of her mom. “I’m learning from the best,” Ava says.
Cook the peppercorns: Preheat the oven to 300˚ F. Bring a small pot of water to a boil over medium heat. Put the peppercorns in a fine-mesh sieve and add to the water; simmer for 2 to 3 minutes. Remove the sieve and let the peppercorns drain. Spread the peppercorns on a baking sheet and place in the oven. Bake until dry, 8 to 10 minutes. (Cooking the peppercorns mellows out their strong flavor.)
Roast the potatoes: Raise the oven temperature to 375˚ F. Toss the potatoes with the olive oil in a large bowl and season with kosher salt. Line a baking sheet with parchment paper. Arrange the potatoes in a single layer on the pan. Put the baking sheet in the center of the oven and roast until the potatoes are browned and tender, 20 to 30 minutes.
Season the steaks: While the potatoes cook, use the bottom of a small skillet to crush the peppercorns on the baking sheet — they should break into coarse crumbs. Season the steaks on both sides with kosher salt, then press them into the crushed peppercorns.
Cook the steaks: Heat a large cast-iron skillet over medium heat until it begins to visibly smoke. Shut the heat off underneath the skillet and use a pair of tongs to place the steaks in the pan in a single layer. Turn the heat to medium and brown the steaks on the first side, 4 to 8 minutes, depending on the thickness. (Resist the temptation to turn them over or move them as they cook!) Flip the steaks using the tongs and brown on the second side, 4 to 6 more minutes. Take the temperature of the steaks using a meat thermometer. Rare registers between 125˚ F and 130˚ F; medium rare is 130˚ F to 135˚ F; and medium is 135˚ F to 140˚ F. Place the steaks on a rack set on a baking sheet to rest while you make your sauce.
Make the sauce: Remove the excess grease from the skillet. Add the butter and shallots and cook, stirring, until translucent, 3 to 5 minutes. Add the vinegar and cook until the liquid reduces almost completely, about 1 minute. Whisk in the mustard and Worcestershire sauce, then add the stock and reduce until decently thickened, 3 to 5 minutes. Taste for seasoning and add salt and pepper, if necessary.
Serve the steaks: Place the steaks on plates and spoon the sauce on top. Arrange the potatoes next to the steaks. Sprinkle with flaky sea salt.