Preheat the oven to 400°F (200°C).

In a skillet, cook the ground lamb (or beef) over medium heat until browned; drain excess fat.

Add diced onion and minced garlic; cook until onion is translucent.

Stir in diced carrots, frozen peas, tomato paste, Worcestershire sauce, and beef broth; simmer until vegetables are tender.

Boil potatoes until soft; drain and mash with milk (or cream) and butter until creamy; season with salt and pepper.

In a baking dish, layer the meat mixture, then spread the mashed potatoes on top.

Bake in the preheated oven for about 20 minutes, or until the top is golden brown.