Prepare the Crust: In a large bowl, whisk together the flours 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.
Caramelize the Onions: Heat olive oil in a large skillet over medium-low heat. Add the sliced onions and cook, stirring occasionally, for 40-50 minutes, or until deeply golden brown and caramelized. Stir in brown sugar, balsamic vinegar, and thyme during the last 5 minutes of cooking.
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. Blind bake the crust for 10 minutes with pie weights.
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.
Bake for 25-30 minutes, or until the crust is golden brown and the cheese is melted and bubbly. Let cool slightly before serving.
Ingredients
6
1 1/4 cups156 gAll-purpose flour
1/4 cup30 gWhole wheat flour
1/2 tsp2.5 mLSalt
3/4 cup170 gCold unsalted butter-cut into cubes
4-6 tbsp60-90 mLIce water
2 tbsp30 mLOlive oil
2 large200 gYellow onions-thinly sliced
1 tsp5 mLBrown sugar
1 tbsp15 mLBalsamic vinegar
1/4 tsp1.25 mLThyme-fresh-chopped
1/2 cup120 mLHeavy cream
1 cup113 gGruyere cheese-aged-shredded
SaltTo taste
Black pepperTo taste
Equipment
Large bowl
Pastry blender or fingers
Large skillet
Rolling pin
9-inch tart pan with removable bottom
Pie weights
Oven
Instructions
Prepare the Crust: In a large bowl, whisk together the flours 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.
Caramelize the Onions: Heat olive oil in a large skillet over medium-low heat. Add the sliced onions and cook, stirring occasionally, for 40-50 minutes, or until deeply golden brown and caramelized. Stir in brown sugar, balsamic vinegar, and thyme during the last 5 minutes of cooking.
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. Blind bake the crust for 10 minutes with pie weights.
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.
Bake for 25-30 minutes, or until the crust is golden brown and the cheese is melted and bubbly. Let cool slightly before serving.
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