Preheat the oven to 375°F (190°C).

Roast the garlic: Cut the top off the garlic head to expose the cloves. Drizzle with olive oil and sprinkle with a pinch of salt. Wrap in aluminum foil and roast for about 30 minutes, until soft and golden. Allow it to cool before handling.

Prepare the dish: Grease a 9×13-inch (23×33 cm) baking dish.

Slice the potatoes: Peel and thinly slice your potatoes, using a mandoline for evenness if available.

Layer the potatoes: Arrange the slices upright in the greased dish, stacking them in layers until all are utilized.

Make the cream mixture: In a saucepan, combine the heavy cream, milk, butter, half of the grated parmesan, thyme, nutmeg, and a pinch of salt and pepper. Heat over medium heat until butter melts and ingredients combine smoothly. Avoid boiling.

Prepare the roasted garlic: Squeeze the softened garlic from the skins, mashing it into a paste. Stir it into the cream mixture until well blended.

Assemble: Pour the creamy mixture evenly over the potatoes in the baking dish. Cover tightly with foil.

Bake: Bake in preheated oven for 40 minutes.

Add cheese topping: Remove the foil, sprinkle the top with shredded Gruyère or mozzarella and remaining parmesan. Bake uncovered for an additional 30 minutes, until bubbly and golden brown.

Cool and serve: Let cool for a few minutes. Garnish with fresh chives before serving. Enjoy!