Preheat the oven to 400°F (200°C)
Peel and chop potatoes
Boil potatoes in salted water until tender
Drain potatoes
Mash potatoes with butter, milk, salt, and pepper
Cook ground lamb or beef in a skillet until browned
Add chopped onion, carrots, and garlic
Cook until vegetables soften
Stir in tomato paste, Worcestershire sauce, salt, and pepper
Add peas and corn
Add beef or lamb broth
Simmer until slightly thickened
Spread the meat mixture in a baking dish
Spoon mashed potatoes over the top
Smooth the potato layer
Optional: rake the top with a fork
Bake until the top is golden and the filling is bubbling
Let rest before serving