5 ounces applewood-smoked bacon, diced
2 teaspoons chopped fresh parsley
Preheat the oven to 350°F.
In a heavy large sauté pan, sauté the bacon over medium heat until just golden brown, about 7 minutes. Using a slotted spoon, transfer the bacon to a bowl, leaving the bacon drippings in the pan.
Add the onions to the pan of bacon drippings and sauté until they are translucent, about 4 minutes. Add the garlic and sauté until the onions are pale golden, stirring often, about 2 minutes. Add the cream, milk, and thyme. Bring the mixture to a simmer. Set aside.
Meanwhile, using a mandoline slicer or a very sharp knife, cut the potatoes crosswise into 1/8-inch-thick slices. Toss the potato slices in a large mixing bowl with the warm cream mixture to coat. Add the salt and black pepper and toss again.
In a 13x9x2-inch baking dish or other 2-quart baking dish, neatly arrange one-fourth of the potato mixture. Sprinkle 1/2 cup of the cheese over. Repeat layering the remaining potato mixture and cheese 3 more times.
Cover with foil and bake for 40 minutes. Remove the foil and bake until the potatoes are tender and golden brown on top, about 20 minutes. You should be able to gently poke a fork through the potatoes when finished.
Let stand for 10 minutes to cool slightly. Sprinkle with the reserved bacon and parsley, and serve.