Instructions

• Preheat the oven to 400°F (use later for baking; you can preheat now or after making the filling).
• Scrub the potatoes clean and place them in a deep pot. Add cold water to cover the potatoes by about 1/2 inch. Add 1/2 teaspoon of the kosher salt (reserve the remaining 1/2 teaspoon of the "1 teaspoon kosher salt, divided" for the mashed potatoes). Bring to a boil over high heat, then reduce to a simmer and cook until a fork easily pierces the potatoes, about 20 minutes.
• Drain the potatoes. While still hot, use a paper towel to rub and remove the skins, then return the potatoes to the warm pot.
• Mash the hot potatoes with a potato masher or handheld mixer. Add the 3 tablespoons butter (cut into chunks) and mash/beat until the butter is incorporated. Add the 1/4 cup half and half and mash/beat until smooth. Season the mashed potatoes with the remaining 1/2 teaspoon kosher salt (from the divided salt) and 1/4 teaspoon freshly ground black pepper. Stir in the 1 cup shredded Irish/white cheddar and the 1/4 cup finely chopped chives. Cover and set aside while you make the filling.
• In a 10-inch oven-safe skillet (or other shallow, wide oven-safe skillet or Dutch oven), heat the 2 tablespoons canola oil over medium heat.
• Add the 1 1/2 cups small diced carrots, 1 cup small diced celery, and the diced white/light-green part of the leek (about 1 cup). Sauté, stirring occasionally, until the vegetables are tender, about 10 minutes.
• Add the 5 cloves garlic (pressed or minced) to the skillet and sauté for 2 minutes more. Transfer the vegetables to a large bowl or plate and set aside.
• Return the skillet to medium heat. Add the 1 1/2 pounds ground beef, breaking it up with a spoon. Season the beef with the separate 1 teaspoon kosher salt and 1/2 teaspoon freshly ground black pepper. Cook until no longer pink, about 5 minutes.
• Stir in the 3 tablespoons tomato paste, 1 tablespoon chopped fresh rosemary, and 1 tablespoon fresh thyme leaves. Cook and stir for 2–3 minutes.
• Return the sautéed vegetables to the skillet with the beef. Sprinkle the 2 tablespoons flour over the mixture and stir to coat evenly. Cook for 1 minute.
• Pour in the 1 cup beef stock, 2 tablespoons soy sauce, and 2 teaspoons Worcestershire sauce. Add the 1 cup frozen peas. Bring the mixture to a boil, then remove from heat. Taste and, if desired, adjust seasoning with salt or pepper.
• Even the meat-and-vegetable mixture in the skillet. Dollop the mashed potatoes over the filling in several portions.
• Use an offset spatula or wooden spoon to spread the mashed potatoes into an even layer over the filling. Sprinkle additional chopped chives on top as desired.
• Place the uncovered skillet in the preheated 400°F oven and bake for 15 minutes. After 15 minutes, turn the oven to broil and broil for up to 5 minutes, watching closely, until the mashed potatoes are lightly browned and the filling is bubbly.
• Remove the skillet from the oven and let the shepherd’s pie rest for 10–15 minutes. Top with more chopped chives if desired and serve.