Preheat oven to 400°F (200°C).
Slice the top off the garlic head, drizzle with olive oil, wrap in foil, and roast for 40 minutes. Squeeze the roasted garlic out of the skins and mash.
Reduce oven temperature to 375°F (190°C).
In a saucepan over medium heat, melt butter. Add cream, milk, roasted garlic, salt, pepper, and nutmeg. Stir until combined and warmed through.
In a greased baking dish, layer half the sliced potatoes. Pour over half the cream mixture and sprinkle with half of the cheeses. Repeat with remaining potatoes, cream, and cheeses.
Cover with foil and bake for 45 minutes. Remove foil and bake for an additional 15 minutes until golden and bubbly.
Let rest for 10 minutes before serving. Garnish with chopped parsley.