Cook the potatoes

• Place the potatoes in a saucepan, cover with salted water and bring to a boil.
• Cook until tender and easily pierced with a knife.

Brown the lamb

• Heat the olive oil in a frying pan over medium-high heat.
• Add the ground lamb and cook, breaking it up, until browned.

Build the filling

• Add the onion, carrots and garlic and cook until softened.
• Stir in the tomato paste and cook briefly.
• Pour in the Worcestershire sauce and beef stock, season with salt and pepper and simmer until thickened.
• Stir in the frozen peas.

Mash the potatoes

• Drain the potatoes and return them to the pan.
• Add the butter and milk and mash until smooth, then season.

Assemble the pie

• Spread the lamb filling in an even layer in a baking dish.
• Spoon the mashed potato over the top and spread it evenly, roughing the surface with a fork.

Bake

• Bake until the top is golden and the filling bubbles at the edges.
• Let rest briefly before serving.