Preheat and prep. Heat your oven to 400°F (200°C). Lightly grease a 9x13-inch baking dish or a deep 10-inch skillet that can go in the oven.

Cook the potatoes. Add the potatoes to a large pot of salted water. Bring to a boil and cook until very tender, about 15 minutes. Drain well.

Make the creamy mash. Return the drained potatoes to the pot. Add butter, cream cheese, and half the milk. Mash until smooth and creamy, adding more milk as needed. Stir in 1/2 cup cheddar. Season with salt and pepper. Set aside.

Sauté the veggies. In a large skillet, warm the olive oil over medium heat. Add onion and carrot with a pinch of salt. Cook until soft and slightly golden, 6–8 minutes. Stir in garlic and cook 30 seconds.

Brown the meat. Add ground lamb or beef. Break it up with a spoon and cook until browned and no longer pink, 5–7 minutes. Drain excess fat if needed. Season with salt, pepper, thyme, and rosemary.

Build the sauce. Stir in tomato paste and Worcestershire; cook 1 minute to caramelize. Pour in beef broth and bring to a simmer. Add the cornstarch slurry, stir, and cook 2–3 minutes until thickened and glossy.

Add peas and adjust. Stir in peas. Taste and adjust salt, pepper, or Worcestershire. The mixture should be savory with a gentle tang and a spoon-coating consistency.

Assemble. Spread the meat mixture in an even layer in your baking dish. Dollop the mashed potatoes over the top, then spread gently to cover edge to edge. Use a fork to create ridges for extra browning.

Cheesy finish. Sprinkle the remaining 1/2 cup cheddar over the potatoes. This gives you that bubbly, golden crust.

Bake. Place the dish on a baking sheet to catch drips. Bake 20–25 minutes, until the top is golden and the filling is bubbling at the edges. For deeper color, broil 1–2 minutes at the end, watching closely.

Rest and serve. Let it rest 10 minutes to set. Sprinkle with parsley if you like. Serve warm with a simple green salad or steamed greens.