Caramelized Onion & Gruyere Tart

Ingredients:
1 recipe of pâte brisée for one 10-inch tart or 1 package of frozen phyllo dough
3 medium red onions, thinly sliced
2 T extra virgin olive oil
1 T unsalted butter
kosher salt
1 teaspoon balsamic vinegar
3/4 cup grated Gruyère Swiss cheese

Preparing the tart:
If making a crust from scratch, prepare and roll out the dough into a tart pan (or roll out the dough on a lightly floured surface to a 10-inch diameter and transfer to a cookie sheet lined with parchment paper); let chill in the refrigerator for a minimum of 1/2 an hour.

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Preparing the filling:
Heat olive oil and butter in a large, heavy-bottomed sauté pan over medium heat, until butter has melted. Add onions, salt, stirring occasionally, until the onions have softened and are translucent (about 10 minutes).

Reduce the heat to medium low and cook for an additional 40 minutes, stirring occasionally, until the onions are well browned. Add balsamic vinegar and cook for another 10 minutes, until onions are completely caramelized. Remove from heat.

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Assembling the tart:
Preheat the oven to 450 degrees F.

Place all but a couple tablespoons of the cheese in the center of the dough. Spread to within 1 1/2 inches from the edges. Add the caramelized onions, layering them on top of the cheese. Fold the edges of the crust dough over so that a small circle of onion is still showing in the center of the tart. Sprinkle the remaining cheese over the top of the tart.

Place in the oven on the middle rack and bake for 10 minutes. Reduce the heat to 350 degrees F and bake for an additional 20-25 minutes, until the crust is golden brown. Remove from oven and let sit for 10 minutes before serving.

Serves 4