Step 1 of 8
Preheat oven to 400°F (200°C).
Step 2 of 8
Boil potatoes until tender, about 20 minutes. Drain and mash with butter and milk.
Step 3 of 8
Meanwhile, brown lamb in a large skillet. Drain excess fat.
Step 4 of 8
Add onion and carrots, cook until softened, about 5 minutes.
Step 5 of 8
Stir in tomato paste, Worcestershire, and broth. Add peas.
Step 6 of 8
Simmer for 10 minutes until thickened.
Step 7 of 8
Transfer meat mixture to a 9x13 baking dish. Spread mashed potatoes on top.
Step 8 of 8
Bake for 25 minutes until potatoes are golden. Let rest 10 minutes before serving.