Step 1

Preheat an oven to 350°F (180°C). Spread the bread cubes on a sheet pan and bake for 15 to 20 minutes, until lightly browned. Set aside.

Step 2

Meanwhile, heat the oil and butter in a large (12-inch/30-cm) sauté pan over medium heat. Add the pancetta and cook for 5 minutes, until it is starting to brown. Stir in the leeks and cook over medium heat for 8 to 10 minutes, until the leeks are tender. Stir in the mushrooms, tarragon, sherry, salt and pepper and cook for 10 to 12 minutes, stirring occasionally, until most of the liquid has evaporated. Off the heat, stir in the parsley.

Step 3

In a large mixing bowl, whisk together the eggs, cream, chicken stock and 1 cup (4 oz./125 g) of the Gruyère. Add the bread cubes and mushroom mixture, stirring well to combine. Set aside at room temperature for 30 minutes to allow the bread to absorb the liquid. Stir well and pour into a 2- to 3-quart (2- to 3-liter) gratin dish about 13 by 9 inches (33 by 23 cm). Sprinkle with the remaining 1/2 cup (2 oz./60 g) of Gruyère and bake for 45 to 50 minutes, until the top is browned and the custard is set. Serve hot. Serves 8 to 10.

Step 4

NOTE: Cut the leeks lengthwise, slice crosswise 1/4 inch (6 mm) thick, wash in a big bowl of water and spin-dry in a salad spinner.

Step 5

Reprinted from Barefoot Contessa Foolproof. Copyright © 2012 by Ina Garten. Photographs copyright © 2012 by Quentin Bacon. Published by Clarkson Potter, an imprint of Random House, a division of Penguin Random House.