Place the finely sliced potatoes into an ice bath and leave to sit for a minimum of 30 minutes and maximum 4 hours. Drain the potatoes and place onto a working surface that is pre-lined with paper towels. Using additional paper towels, press down onto the potatoes to remove as much moisture as possible.
Preheat the oven to 180 degrees C.
In a medium sized saucepan on a low heat, combine the cream, milk, garlic and thyme and bring to a low simmer. Simmer for 10 minutes or until slightly thickened.
In a large circular baking dish, rub the butter all over the edges and bottom. Begin to layer the potatoes and season with salt and pepper after every layer. Pour the cream mixture over the potatoes and then sprinkle with the cheese. Cover the dish with alfoil and bake for 2 hours. Remove the al-foil and bake for a further 15 minutes or until the cheese is bubbling and golden.
Leave to sit for 20 minutes before cutting into it. Sprinkle with fresh parsley and serve.