Pommes Boulangère

Instructions

1. 1

   Heat 3 tablespoons butter in a medium nonstick pan over medium-high. When the butter is melted and foamy, add the onion and cook, stirring occasionally, until soft and translucent, 8 to 10 minutes. Reduce the heat to medium and continue to cook, stirring often, until deeply golden brown, adding a splash of water as needed should the bottom begin to catch. This will take 25 to 30 minutes more. Season with salt and pepper, scrape into a medium bowl, and set aside.

2. 2

   Arrange an oven rack in the centre position and heat the oven to 200C / 180C fan. Rub the bottom and sides of a 3-litre baking dish with the cut sides of the garlic clove, then coat generously with room temperature butter.

3. 3

   Using a mandoline or a sharp knife, slice about a third of the potatoes into 3mm rounds. Working swiftly so they do not discolour, heat 1 tablespoon butter in the reserved pan over medium-high, add the sliced potatoes, and toss until well coated. Season lightly with salt and pepper, then cook, tossing occasionally, until browned in spots and just beginning to turn translucent, about 5 minutes. Scrape into a large bowl.

4. 4

   Working in two batches, slice the remaining potatoes and cook with the remaining butter just as before. Transfer all to the same bowl and allow to cool briefly.

5. 5

   Scatter about a third of the potato slices in an even layer on the bottom of the prepared dish, then arrange about half the onions over the top with a few pinches of Herbs de Provence and a sprig of thyme. Scatter half the remaining potatoes, then the remaining onions. Layer the final potatoes on top, shingling them in a rosette or leaving them pleasingly haphazard as you see fit.

6. 6

   Add the stock to the reserved pan and bring to a simmer over medium-high heat. Taste and season well. Remove from the heat and pour the stock gently into the baking dish until it barely covers the potatoes. Reserve any excess for moistening during the bake.

7. 7

   Transfer to the oven and bake uncovered until the potatoes are tender and golden and the stock is bubbling, reduced, and largely absorbed, 1 hour 20 minutes to 1 hour 40 minutes. Should the surface appear to be drying out, add a little of the reserved stock.

8. 8

   Remove from the oven and allow to cool entirely at room temperature. While cooling, introduce the truffle oil so it may be properly absorbed into the layers. The dish may rest uncovered at room temperature for several hours without objection.

9. 9

   About an hour before serving, heat the oven to 180C / 160C fan. Return the dish to the oven and bake uncovered until heated through, 20 to 25 minutes. Serve warm.