Rustic Onion Tart

Ingredients

• 1 recipe for butter sour cream pastry dough or 1 packaged, flat pie crust
• 3 medium sized red and/or yellow onions
• 2 tablespoons extra virgin olive oil
• 1 tablespoon butter
• Salt
• 1 teaspoon balsamic vinegar
• 1/2 teaspoon fresh thyme, chopped, or 1/4 teaspoon dried thyme
• 3/4 cup roughly grated Gruyère Swiss cheese
• 1 1/4 cup all purpose flour
• 1 teaspoon salt
• 5 ounces of butter, cubed
• 1/4 cup sour cream

Directions

1. If you’re making the crust yourself, start there: mix the dough and tuck it into the refrigerator to chill while the onions cook.
2. For the dough, combine the flour and salt in a large bowl with a whisk. Work in the butter, using your fingers or a pastry cutter, until the mixture looks like rough crumbs.
3. Stir in the sour cream with a fork until the dough comes together. Press it into a ball, flatten it into a disk, cover it in plastic wrap, and refrigerate it for at least an hour.
4. Peel the onions, then cut them lengthwise, from the stem end down through the root end.
5. Warm the olive oil and butter in a large sauté pan with a heavy bottom over medium heat. When the butter is melted, stir in the onions and season them with a little salt.
6. Cook the onions for 10 minutes, stirring here and there, until they are soft and translucent.
7. Lower the heat to medium low and continue cooking for 40 minutes, stirring now and then, until the onions are deeply browned.
8. Stir in the balsamic vinegar and cook for 10 minutes longer, until the onions are fully caramelized. Take the pan off the heat.
9. Heat the oven to 450 degrees F. Take the dough out of the refrigerator and let it rest for 5 minutes before you roll it.
10. On a lightly floured surface, roll the dough into a 13-inch round. Move it onto a parchment-lined cookie sheet.
11. Scatter all but a couple tablespoons of the cheese in the middle of the dough, leaving 1 1/2 inches bare around the edge. Spoon the caramelized onions over the cheese, then sprinkle the thyme on top.
12. Fold the dough border up over the filling, pleating as you go, so a small round of onion remains visible in the center. Scatter the reserved cheese over the tart.
13. Bake the tart on the middle rack at 450 degrees F for 10 minutes. Turn the oven down to 350 degrees F and bake for another 20-25 minutes, until the crust is golden brown.
14. Take the tart out of the oven and leave it to sit for 10 minutes before serving.