Caramelized Onion and Gruyere Tart

This tart is a vehicle for two winter-friendly ingredients – caramelized onions and Gruyère cheese. Caramelized onions are sweet, savory, and slick. A lengthy cooking time coaxes out their abundant natural sugars and releases their juices, resulting in a squidgy heap of golden brown onions. Gruyère cheese is a nutty, piquant Swiss cheese, and a favorite melting cheese in fondue. Combine the two ingredients, and you have the makings for a richly savory and rustic winter meal, guaranteed to spark visions of snowflakes and crackling fires in your imagination (at least in mine, since I live in California!)

There are few ingredients in this simple creation, so every ingredient counts. Take the time to properly brown the onions, about 45 minutes in all, and choose an authentic Gruyère cheese, preferably aged for deep flavor – and you will be rewarded with this simple and seductive tart. Serve it as a light meal, or cut into thin slivers and pass around as an appetizer.

Caramelized Onion and Gruyère Tart

Serves 6 to 8

Dough:
1 cup all-purpose flour
1/2 teaspoon salt
6 tablespoons chilled unsalted butter, cut into 1/4-inch cubes
3 tablespoons ice water

Filing:
2 tablespoons olive oil
2 pounds yellow onion, peeled and thinly sliced
1 teaspoon salt
2 tablespoons Calvados (apple brandy)
1/2 teaspoon freshly ground black pepper
3 ounces finely grated Gruyère cheese
1 teaspoon fresh thyme, plus extra for garnish
1 egg, slightly beaten

1. Prepare the crust: Combine the flour and salt in a food processor and pulse once or twice to combine. Add the butter and pulse until the dough resembles coarse meal, with some pieces of the butter visible. Add the water and pulse once or twice – just until the dough comes together, adding another tablespoon of water if necessary. Dump the dough onto a work surface and form it into a disk. Wrap in plastic and refrigerate for at least 1 hour.
2. Preheat the oven to 375°F.
3. Heat the olive oil over medium heat in a deep skillet or pot. Add the onions and salt and cook the onions, until they are golden brown, soft and squidgy, 35 to 40 minutes, stirring occasionally. Add the Calvados and black pepper and cook until the liquid evaporates, 1 to 2 minutes, stirring frequently. Remove from the heat and cool while you roll out the dough.
4. Roll out the dough to fit in the bottom and up the sides of a 10-inch round tart tin with a removable bottom. Sprinkle half of the cheese over the bottom of the tart. Spread the onions in the shell and sprinkle the thyme over the onions. Brush the exposed crust rim with the egg wash. Sprinkle the tart and crust with the remaining cheese.
5. Bake the tart until the crust is firm and golden and the onions are deeply colored without blackening, about 30 minutes. Remove and cool slightly. Serve slightly warm or at room temperature garnished with additional thyme.