Aunt Hortense's Caramelized Onion & Gruyere Tart

Instructions

1. Prepare the Crust: In a large bowl, whisk together the flour and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs. Gradually add ice water, 1 tablespoon at a time, mixing until the dough just comes together. Form the dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.
2. Caramelize the Onions: Heat olive oil in a large skillet over medium-low heat. Add the sliced onions and cook, stirring occasionally, for 30-40 minutes, or until deeply golden brown and caramelized. Stir in brown sugar and thyme during the last 5 minutes of cooking.
3. Assemble the Tart: Preheat oven to 375°F (190°C). Roll out the chilled dough on a lightly floured surface to a 12-inch circle. Transfer the dough to a 9-inch tart pan with a removable bottom. Trim and crimp the edges.
4. Spread the caramelized onions evenly over the tart crust. Pour the heavy cream over the onions. Sprinkle with Gruyere cheese. Season with salt and pepper.
5. Bake for 25-30 minutes, or until the crust is golden brown and the cheese is melted and bubbly. Let cool slightly before serving.