1. Crush the garlic into a paste with the salt. In a large pan, combine the garlic paste, cream, milk and white pepper.
2. Add the sliced potatoes, turning into the cream mixture to ensure all the slices are evenly coated. Bring to the boil, then simmer for 15 minutes until the potatoes are tender and the mixture has thickened.
3. Butter a ovenproof dish (9×13 or bigger). Gently pour the potatoes into the dish and level the top. Sprinkle over the grated Parmesan and place in a preheated oven at 150°C (300°F) for about 1 hour, until the top is nicely golden.