2 Tbsp unsalted butter (plus more for baking dish)
1 clove of garlic, peeled and crushed or pressed
3 lbs Yukon Gold potatoes, scrubbed, peeled, and thinly sliced
1-1/4 Cups whole milk
1-1/4 Cups heavy cream
1 tsp coarse sea salt
1/2 tsp ground black pepper
Preheat oven to 350 F. Butter the inside of a 2-quart, ovenproof shallow baking dish, and rub the greased surface with the crushed garlic. Layer potato slices in prepared baking dish, overlapping the pieces slightly.
Meanwhile, in a small bowl, whisk together the milk, heavy cream, salt, and ground pepper. Pour the cream mixture over the potato slices. Dot the surface with chunks of cold butter and cover the baking dish with foil.
Place the baking dish on a rimmed baking sheet, and bake, covered, on the top rack of the oven until potatoes are fork-tender, about 1 hour. Uncover the dish for another 30 minutes, and bake until top layer of potatoes appear golden brown in spots.
Remove dish from the oven and allow to rest 20 minutes before serving.
Make ahead, take-along: Prepare and assemble the dish up to 8 hours in advance. Allow dish to warm to room temperature before baking. Can share oven space with main dish (ham or turkey are especially yummy) for the last 90 min of the main course cooking.