Step 1

Heat the oven to 350°F (175°C). Adjust the oven rack to the middle position and line a rimmed baking sheet with foil.

Step 2

Melt the butter In a medium skillet set over medium heat, and sauté the shallots until soft and golden brown, 5 to 10 minutes. Scrape the shallots into a bowl, toss in the ham, and stir to combine.

Step 3

Rub the garlic clove over the bottom and sides of a 2-quart baking dish or gratin dish. Let the dish rest for a few minutes and then rub the bottom and sides of the dish with butter.

Step 4

Peel the potatoes and slice them crosswise about 1/8 inch (3 mm) thick. A mandoline or handheld slicer makes short work of this.

Step 5

Arrange an overlapping layer of potatoes, like a splayed deck of cards, in the bottom of the gratin dish. Season with salt and pepper to taste. Sprinkle about 1/3 of the ham and shallot mixture over the potatoes and then about 1/3 of the cheese. Continue layering the potatoes, ham and shallot mixture, and cheese, seasoning each layer with salt and pepper and finishing with the cheese. (You should have 3 sets of layers.) Gently press down on the casserole if it’s threatening to rise above the edge of the baking dish.

Step 6

Place the dish on the foil-lined rimmed baking sheet and drizzle the cream all along the sides of the dish being careful not to move the cheese. Stop adding cream when you see it rising alongside the potatoes but isn’t drowning them.

Step 7

Slip the casserole, uncovered, in the oven and bake until the cream bubbles happily along the edge of the dish, the top is crisp and golden, and a knife easily pierces all the layers, 60 to 80 minutes. Let stand for 10 minutes before serving.