Preheat your oven to 400°F (200°C).
Bring a large pot of salted water to a boil. Add the potatoes and cook until fork-tender, about 15 minutes. Drain, then return to the pot. Add butter and milk, and mash until smooth and creamy. Season with salt and pepper. Set aside.
4 large potatoes, ½ cup milk, 4 tablespoons butter, Salt and pepper
In a large skillet, heat olive oil over medium heat. Add onions and carrots, cooking for about 5 minutes until softened. Stir in the ground lamb and cook until browned, breaking it apart with a spoon.
1 cup onion, 2 carrots, 1 tablespoon olive oil, 1 pound ground lamb
Mix in the tomato paste, Worcestershire sauce, beef broth, and peas. Cook for another 5 minutes until everything is well combined and heated through. Season with salt and pepper to taste.
1 cup frozen peas, 2 tablespoons tomato paste, 1 cup beef broth, 1 tablespoon Worcestershire sauce, Salt and pepper
Transfer the lamb mixture into a baking dish, spreading it evenly. Spoon the mashed potatoes on top and smooth them out with a spatula. Use the back of a spoon to create peaks for extra crispy edges.
Bake for 30–40 minutes, until the potatoes are golden and the filling is bubbling. Let cool slightly before serving.