Step 1

Heat the oven. Arrange a rack in the middle of the oven and heat the oven to 375°F.

Step 2

Slice and boil the potatoes. Peel 2 1/2 pounds Yukon gold potatoes and cut into 1/4-inch thick slices with a mandoline or knife. Place the potatoes and 1 tablespoon of the kosher salt in a large pot and add enough cold water to cover them by 1 inch. Bring to a boil over high heat. Reduce the heat to medium and simmer just until the potatoes are barely tender, 4 to 5 minutes. (The potatoes will continue cooking in the oven. Do not overcook.)

Step 3

Drain the potatoes. Drain the potatoes and let cool while you make the filling. Dry the pot with a paper towel, but no need to wash.

Step 4

Prep the filling ingredients. As the potatoes are cooling, finely grate 2 ounces Gruyère cheese (about 1/2 cup). Mince 3 garlic cloves, dice 1 medium yellow onion (about 1 1/2 cups), and finely chop until you have 1 tablespoon fresh thyme leaves. Cut 6 slices thick-cut bacon crosswise into 1/2-inch pieces. Cut 1 wheel semi-soft cheese into 12 wedges.

Step 5

Cook the bacon. Add the bacon to the empty pot and cook over medium heat, stirring occasionally, until the bacon is browned and crisp, 10 to 15 minutes. Using a slotted spoon, transfer the bacon to a bowl. Pour the bacon fat into a small heat-proof bowl, then measure out 2 tablespoons and return it to the pot.

Step 6

Cook the onions and garlic. Add the onion and garlic to the pot and cook over medium heat, stirring frequently, until softened and very fragrant, 3 to 5 minutes. Add the thyme, remaining 1 teaspoon kosher salt, and 1/2 teaspoon black pepper. Cook until fragrant, 2 to 3 minutes.

Step 7

Deglaze with white wine and add the cream. Add 1/2 cup dry white wine and scrape up any browned bits from the bottom of the pot with a wooden spoon. Bring the wine to a simmer and cook until reduced by half, 2 to 4 minutes. Add 1 1/2 cups heavy cream and bring to a simmer. Let simmer for 2 minutes, then remove from the heat.

Step 8

Assemble the first layers. Arrange half of the potato slices in an even layer in a 9x13-inch or other 4-quart baking dish. Sprinkle half of the bacon evenly over the top. Pour half of the cream mixture over the bacon and spread the onions out into an even layer.

Step 9

Finish assembling the tartiflette. Arrange the remaining potato slices over the onions. Pour the remaining cream mixture the potatoes and spread the onions out into an even layer. Sprinkle with the Gruyère cheese, place the cheese wedges on top, and sprinkle with the remaining bacon.

Step 10

Bake the tartiflette. Bake until the cheese is browned and the filling is bubbling, 30 to 35 minutes. Let cool for 10 minutes before serving.