Preheat your oven to 180°C (356°F) on the fan-forced setting.
Grate the garlic cloves into the melted butter and mix this with the thickened cream.
Prepare your ingredients by chopping the rosemary and grating the cheese. Have your baking dish ready.
Thinly slice the potatoes using a mandolin.
Begin layering the potatoes in your baking dish. Start with a layer of potatoes, then add grated Pecorino cheese, salt, pepper, chopped rosemary, and a drizzle of the garlic butter and cream mixture.
Repeat the layering process until all the potatoes and seasonings are used.
Cover the dish with foil and bake in the oven for at least 1 hour and 20 minutes, or until the potatoes are fully cooked and a knife passes through them easily.
Remove the foil, grate more Pecorino cheese on top, and place the dish back under the grill of the oven for 10-12 minutes or until it's golden brown and delicious.
Let the potato bake rest for 10-15 minutes before serving. Enjoy!