This tart is a vehicle for two winter-friendly ingredients -- caramelized onions and Gruyere 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. Gruyere cheese is a nutty, piquant Swiss cheese, a favorite melting cheese in fondue, and equally delicious au naturel. Combine the two ingredients, and you have the makings for a richly savory winter meal, guaranteed to spark visions of snowflakes and crackling fires in your imagination. (At least in mine, since I live in California!)
This recipe is my best reproduction of an appetizer I ate years ago, when I lived in a Swiss winter wonderland near Geneva. It was a complimentary sliver of tart, passed around with a pre-dinner drink at a local auberge in the hills overlooking Lake Geneva. I have never forgotten this tart. It was simple and rustic, just like the half-timbered dining room in which it was served, with its man-size fireplace and crooked beamed ceiling.
There are few ingredients in this minimal creation, so every ingredient counts. Take the time to properly brown the onions and choose an authentic Gruyere cheese, preferably aged for deep flavor -- and you will be rewarded with this uncomplicated and seductive tart. Serve it as a light meal, or cut into thin slivers and pass around as an appetizer.
Caramelized Onion and Gruyere Tart
Active time: 25 minutes
Total time: 2 hours
Yield: 6 to 8 servings
1 cup all-purpose flour
1/2 teaspoon salt
6 tablespoons chilled unsalted butter, cut into 1/4-inch cubes
3 tablespoons ice water
2 tablespoons olive oil
2 pounds yellow onions, peeled and thinly sliced
1 teaspoon salt
2 tablespoons Calvados (apple brandy)
1/2 teaspoon freshly ground black pepper
3 ounces finely grated Gruyere cheese, divided
1 teaspoon fresh thyme, plus extra for garnish
1 egg, slightly beaten
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.
Heat the oven to 375 degrees.
Heat the olive oil over medium in a deep skillet or pot. Add the onions and salt; cook until the onions 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.
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 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.
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.
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