Step 1

With the rack in the middle position, preheat the oven to 375°F (190°C). Line an 8-inch (20 cm) square pan with a strip of parchment paper, letting it hang over two sides.

Step 2

In a pot, bring the cream and garlic to a boil. Simmer for 5 minutes over low heat. Season with salt and pepper.

Step 3

Place the potato slices in a large bowl. Strain the cream directly over the potatoes. Compost the garlic. Mix the potatoes well. Adjust the seasoning.

Step 4

Layer the potatoes into the prepared pan, letting the slices overlap. Pour the garlic cream into the pan. Cover the potatoes with a square of parchment paper. Cover the pan with foil. Bake for 1 hour 30 minutes or until the potatoes are very tender. Let cool.

Step 5

Place a second 8-inch (20 cm) square pan on the potatoes, leaving the parchment paper and foil in place. Place heavy weights, such as cans of food, into the second pan to press the potatoes down. Let cool completely in the refrigerator for 8 hours or overnight.

Step 6

Remove the parchment paper and foil. Place the gratin on a work surface. Cut the sides slightly to straighten them out, if desired. Cut the gratin in half, then cut each half into 6 rectangles, to get a total of 12 pieces. Freeze at this point, if desired.

Step 7

With the rack in the middle position, preheat the oven to 400°F (200°C). Line a baking sheet with a silicone mat or parchment paper.

Step 8

In a large non-stick skillet over medium-high heat, brown half of the gratin pieces at a time on all sides in half of the oil. Place the thyme sprigs in the skillet to flavour the oil. Transfer the gratin to the baking sheet. Bake for 8 minutes or until the gratin pieces are heated through and very crispy.