Preheat the oven to 375°F (190°C).

Place garlic cloves in a 9-inch cake pan and drizzle with olive oil.

Cover the pan with foil and roast for 40 minutes, or until the garlic is tender.

Let the garlic cool slightly, then squeeze out the roasted cloves.

Mash the roasted garlic into a paste.

Transfer the garlic paste to a saucepan.

Add half-and-half, chopped thyme, and chopped rosemary to the saucepan.

Bring the mixture to a boil, then reduce the heat to low and simmer for 20 minutes, or until the liquid has reduced to 3 cups.

Season the cream mixture with salt and pepper.

Thinly slice the Yukon Gold potatoes.

Shred the aged Manchego and San Simon (or smoked Gouda) cheeses.

Arrange one-fourth of the potato slices in the bottom of a 9x13 inch baking dish.

Top the potatoes with one-fourth of the shredded cheeses.

Drizzle lightly with the garlic cream.

Repeat the layering with the remaining potatoes, cheese, and cream, ensuring the potatoes are submerged in cream.

Pour any remaining cream on top.

Bake the gratin for about 1 1/2 hours, or until golden brown and bubbling.

Let the gratin cool for 20 minutes before cutting into squares and serving.