Makes 6 main-course or 10 first-course servings
- 2 cups all-purpose flour
- 1 stick (1/2 cup) cold unsalted butter, cut into 1/2-inch cubes
- 1/4 cup vegetable shortening
- 1/2 teaspoon salt
- 4 to 5 tablespoons ice water
- 4 bacon slices (1/4 lb), cut crosswise into 1/8- to 1/16-inch-wide strips
- 3 tablespoons unsalted butter
- 2 lb onions, halved lengthwise and very thinly sliced crosswise (10 cups)
- 1 1/4 teaspoons salt
- 1 teaspoon black pepper
- 1 cup crème fraîche or heavy cream
- 4 large eggs
- 1/2 teaspoon freshly grated nutmeg
Blend together flour, butter, shortening, and salt in a bowl with your fingertips or a pastry blender (or pulse in a food processor) just until most of mixture resembles coarse meal with some small (roughly pea-size) butter lumps. Drizzle evenly with 4 tablespoons ice water and gently stir with a fork (or pulse in processor) until incorporated.
Squeeze a small handful: If it doesn’t hold together, add more ice water, 1/2 tablespoon at a time, stirring (or pulsing) until just incorporated, then test again. (Do not overwork mixture, or pastry will be tough.)
Turn out mixture onto a lightly floured surface and divide into 6 equal portions. With heel of your hand, smear each portion once or twice in a forward motion. Gather dough together with pastry scraper and press into a ball, then flatten into a disk. Chill dough, wrapped in plastic wrap, until firm, at least 1 hour.
Roll out dough on a floured surface with a floured rolling pin into a 14-inch round and fit into tart pan. Trim excess dough, leaving a 1/2-inch overhang, then fold overhang over pastry and press against side to reinforce edge. Lightly prick bottom with a fork and chill until firm, about 30 minutes.
Put oven rack in middle position and preheat oven to 400°F.
Line chilled shell with foil and fill with pie weights. Bake until pastry is set and pale golden along rim, 15 to 20 minutes. Carefully remove foil and weights and bake shell until golden all over, 10 to 15 minutes more. Transfer shell to a rack. (Leave oven on.)
Prepare filling while shell bakes:
Cook bacon in a 12-inch nonstick skillet over moderate heat, stirring occasionally, until crisp, 6 to 8 minutes. Transfer bacon with a slotted spatula to paper towels to drain and pour off bacon fat. Add butter to skillet and cook onions with 3/4 teaspoon salt and 1/2 teaspoon pepper over moderate heat, stirring, until just wilted, about 2 minutes. Cover surface of onions with a round of parchment or wax paper (or cover skillet with a tight-fitting lid) and continue to cook, lifting parchment to stir frequently, until onions are very soft and pale golden, about 20 minutes. Stir in bacon, then remove from heat and cool 10 minutes.
Whisk together crème fraîche, eggs, nutmeg, remaining 1/2 teaspoon salt, and remaining 1/2 teaspoon pepper in a large bowl, then stir in onions.
Fill and bake tart:
- Pour filling into tart shell, spreading onions evenly, and bake until filling is set and top is golden, 25 to 35 minutes. Serve warm or at room temperature.