Potato gratin

Position one oven shelf towards the base of the oven for the potatoes, and then the shelf above it fairly high for the lamb. Set the oven to 220°C or Gas Mark 7.

Tip the cream and milk into a saucepan and add the stock cube, garlic, mustard and seasoning. Bring the mixture to the boil then add the potatoes and onion to the pan. Bring the mixture to a gentle simmer, and cook for 10 minutes, stirring it occasionally to make sure that the cream doesn't burn on the bottom of the pan.

Tip mixture into an ovenproof gratin dish. Cover dish with foil, place it on lower oven shelf and cook potatoes for 30 minutes.

Remove the foil and scatter the cheese over the top. Return the dish to the oven and bake the gratin for a further 20-30 minutes, or until the cheese is a light golden colour.

Remove the dish from the oven and serve the potatoes immediately, or turn the oven off and leave the potatoes inside for up to a further 10-15 minutes if the guests are still eating the starter.