Rustic onion tart

First made Thanksgiving 2008. Adapted from the Simply Recipes recipe. We added prosciutto to the filling, and swapped mozzarella in for some of the Gruyere cheese. Like the chicken pot pie recipe, the tart crust is made partially with vodka for a flakier texture.

Tart crust

 * 1 1/4 cups all-purpose flour, plus extra for rolling
 * 8 Tbsp (1 stick) unsalted butter, very-cold, cut into 1/2 inch cubes
 * 1/2 teaspoon salt
 * 1/2 teaspoon sugar (increase to 1 1/2 teaspoons if for a sweet recipe)
 * 1 to 2 Tbsp ice water, very cold
 * 1 to 2 Tbsp vodka, very cold

Filling

 * 3 medium sized red onions
 * 2 Tbsp olive oil
 * 1 Tbsp butter
 * Salt
 * Several slices of prosciutto
 * 1 teaspoon high-quality balsamic vinegar
 * 1/4 cup roughly grated Gruyere Swiss cheese
 * 1/2 cup roughly grated mozzarella cheese

Tart crust

 * 1) Start by cutting the sticks of butter into 1/2-inch cubes and placing in the freezer for at least 15 minutes (preferably longer) so that they become thoroughly chilled.
 * 2) In a food processor, combine flour, salt, and sugar, pulse to mix. Add butter and pulse 6 to 8 times, until mixture resembles coarse meal, with pea size pieces of butter. Add water and vodka 1 tablespoon at a time, pulsing until mixture just begins to clump together. If you pinch some of the crumbly dough and it holds together, it's ready, if not, add a little more water and pulse again.
 * 3) Remove dough from machine and place on a clean surface. Carefully shape into a discs. Do not over-knead the dough! You should still be able to see little bits of butter in the dough. These bits of butter are what will allow the result crust to be flaky. Sprinkle the disc with a little flour on all sides. Wrap the disc in plastic wrap and refrigerate at least 1 hour.
 * 4) Remove the crust disk from the refrigerator. Let sit at room temperature for 5-10 minutes. Sprinkle some flour on top of the disk. Roll out with a rolling pin on a lightly floured surface to a 12 inch circle; about 1/8 of an inch thick. As you roll out the dough, use a metal spatula to check if the dough is sticking to the surface below. Add a few sprinkles of flour if necessary to keep the dough from sticking. Gently fold in half. Place on to a 9-inch pie plate, lining up the fold with the center of the pan. Gently unfold and press down to line the pie dish with the dough.

Filling

 * 1) Peel and slice the onions.
 * 2) Heat olive oil and butter in a large, heavy-bottomed sauté pan on medium heat. Once the butter has melted, add the onions and sprinkle a little salt over them. Cook, stirring occasionally for 10 minutes, until the onions have softened and are translucent. 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 10 minutes more, until onions are completely caramelised. Remove from heat.
 * 3) Preheat the oven to 450°F. Remove the dough from the refrigerator and let stand for 5 minutes before rolling it out. Roll out the dough on a lightly floured surface to a 10-inch diameter. Remove the crust dough to a cookie sheet lined with parchment paper.
 * 4) Place all but a couple tablespoons of the cheese in the centre of the dough. Spread to within 1 1/2 inches from the edges. Add the caramelised 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 centre of the tart. Sprinkle the remaining cheese over the top of the tart.
 * 5) Place in the oven on the middle rack. Bake for 10 minutes at 450°F. Reduce the heat to 350°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 4-6.