Potato-Bacon Gratin

Directions

1. 1
   Preheat the oven to 350F.
2. 2
   Cut the bacon into 3/8-inch-thick slices, and stack them in two piles, then cut the bacon crosswise into 3/8-inch even-sided rectangular shapes, or lardons.
3. 3
   Heat a large saute pan or Dutch oven over medium-high heat for a minute.
4. 4
   Swirl in the olive oil and add the bacon.
5. 5
   Cook the bacon about 5 minutes, stirring often, until tender and lightly crisped.
6. 6
   Remove to a plate with a slotted spoon, reserving the bacon fat in the pan.
7. 7
   Add the onions, 2 teaspoons thyme, 1 teaspoon salt, and some pepper to the pan.
8. 8
   Cook 15 minutes, stirring and scraping with a wooden spoon, until the onions start to caramelize.
9. 9
   Turn the heat down to low, and continue to cook, about 10 minutes, stirring often, until the onions are a deep golden brown.
10. 10
    Remove from the heat and set aside.
11. 11
    Use a mandoline to slice the potatoes into 1/16-inch-thick rounds.
12. 12
    Pour 1/2 cup cream evenly onto the bottom of a 9-by-9-inch (or equivalent) gratin dish.
13. 13
    Place one layer of potatoes side by side, slightly overlapping, on the bottom of the dish.
14. 14
    Spread a third of the onions over them and scatter a third of the bacon on top.
15. 15
    Arrange a second layer of potatoes, drizzle a 1/4 cup cream over it, and season with 1/4 teaspoon salt, a healthy pinch of pepper, and 1 teaspoon thyme.
16. 16
    Press the potatoes down with your fingers, letting the cream soak up through the layers.
17. 17
    This will ensure that the cream is evenly distributed and coats the potatoes well.
18. 18
    Arrange another layer of potatoes on top, followed by another third of the caramelized onions and the bacon.
19. 19
    Drizzle over another 1/4 cup cream, and continue with two more layers of potatoes.
20. 20
    Drizzle with 1/2 cup cream and season with 1/4 teaspoon salt and a pinch of pepper.
21. 21
    Press the potatoes down with your fingers again.
22. 22
    Scatter the rest of the onions and bacon over the potatoes, and drizzle with 1/3 cup cream.
23. 23
    Season one last time with 1/4 teaspoon salt, 1 teaspoon thyme, and a pinch of pepper.
24. 24
    The cream should cover the potatoes but not be soupy.
25. 25
    Add more cream if the gratin seems dry.
26. 26
    Cover tightly with aluminum foil.
27. 27
    Bake 1 1/2 hours, until the potatoes are tender when pierced.
28. 28
    Remove from the oven, and carefully uncover.
29. 29
    Turn the oven up to 425F and return the gratin to the oven.
30. 30
    Cook another 20 minutes or so, until the top is nice and golden brown (as in gratineed).