Tip the double cream, milk and garlic cloves into a large saucepan and bring to a simmer.
Slice the large potatoes very finely, about 3-4mm, add them to the cream and simmer for 5 mins or until just cooked.
Gently stir to separate the potato and stop it sinking and catching on the bottom of the pan.
Remove the potatoes with a slotted spoon and place in a wide shallow ovenproof dish. Season with salt and pepper between each layer until they are about 5cm in depth.
Pour over the garlic-infused cream (discarding the garlic) – just enough to seep through the layers and leave a little moisture on the surface.
Scatter over the grated cheese, then bake for 30 mins until the potatoes are soft and browned – increasing the heat for the last 10 mins to brown the crust.