Tip the milk, double cream, thyme sprigs and garlic cloves into a large saucepan and bring to a simmer.

Next add the sliced potatoes and simmer for 4-6 minutes or until just cooked. Gently stir the potatoes regularly to stop them sticking to each other and the saucepan.

Remove the potatoes from the saucepan with a slotted spoon and place in shallow ovenproof dish. (I did continue to allow the cream to cook for another 5-10 minutes to reduce its consistency but you can choose not to).

Scatter over the grated cheese, if using, then bake for 40 mins or until the potatoes are soft and browned. Increase the heat for 5-10 mins if not brown enough.