Preheat the oven to 180 degrees Celsius.

Chop the onion and add to a large saucepan with the olive oil and put on a medium heat. Add the roughly sliced mushrooms.

Sizzle for a couple of minutes, then add the leftover lamb and sliced carrots. Pour over the leftover gravy and add about the same amount again of water. Add the frozen peas, bring to a simmer, stir in the mint and then turn off the heat.

Put the leftover dauphinoise potatoes in another saucepan and add the butter. Put on a low heat (so the butter will melt) and mash well until smooth, then turn off the heat.

Pour your lamb filling into a casserole dish, then carefully pile on the mash. Even out with a fork, then sprinkle over the grated cheese.

Bake in the oven for around 30 minutes, until it’s bubbling and the top is golden brown.