Scalloped Potatoes and Leeks with Herbs

Preheat an oven to 375°F (190°C).

In a saucepan over medium heat, melt the butter. Whisk in the flour and cook, whisking constantly, until golden, about 2 minutes. Slowly whisk in the milk, making sure each addition is fully incorporated before adding more. Remove from the heat and stir in the crème fraîche. Season to taste with salt and pepper. Cover the sauce and keep warm.

In a 5 1/2-quart (5.5-l) Dutch oven over medium heat, warm the olive oil. Add the leeks and cook, stirring occasionally, until tender, about 5 minutes. Add the garlic, chopped thyme, rosemary and sage and cook, stirring occasionally, until fragrant, about 1 minute. Add the wine and cook, stirring occasionally, until reduced by half, about 4 minutes. Remove from the heat.

Stir about 1 1/2 cups (12 fl. oz./375 ml) of the sauce into the pot with the leek mixture. Arrange about a third of the potato slices in a single layer, slightly overlapping, on top of the leeks. Season generously with salt and pepper and spread a third of the remaining sauce on top. Repeat twice more to use all the remaining potatoes and sauce, seasoning each layer with salt and pepper. Sprinkle evenly with the cheese and arrange the thyme sprigs on top.

Bake until the potatoes are tender, about 1 hour. Let stand for about 10 minutes, then garnish with fried sage leaves, if using, and serve. Serves 10.

Williams Sonoma Test Kitchen