For quicker quiche assembly, make the dough and line the tart pans the day before, but save baking for the day you serve them—they’re ideally served warm. You’ll need six 4-inch tart pans to make these quiches.
- 2¼ cups all-purpose flour
- ½ teaspoon kosher salt
- 14 tablespoons unsalted butter 1 stick plus 6 tablespoons, cut into pieces and chilled
- ¼ to ⅓ cup ice water
- 2 tablespoons unsalted butter
- 3 shallots thinly sliced
- 1 medium leek light green and white parts only, halved lengthwise and thinly sliced
- 1 medium onion thinly sliced
- 3 to 4 sprigs fresh thyme roughly chopped
- 3 large eggs lightly beaten
- 1 cup grated aged Gouda
- ½ cup heavy cream
- ½ cup whole milk
- 1 tablespoon whole-grain mustard
- ¾ teaspoon kosher salt plus more to taste
- Freshly ground black pepper to taste
- Add flour and salt to the bowl of a food processor and pulse a few times to combine. Add butter and pulse until butter is in pea-size pieces. Add ¼ cup ice water and pulse until dough comes together. (Add additional water, a tablespoon at a time, as necessary.) Handling the dough as little as possible, transfer to a clean work surface and pat it together. Divide in half and shape into 2 disks. Wrap with plastic wrap and refrigerate at least 1 hour or overnight.
- Heat oven to 375ºF. Divide each disk into 3 pieces. Place 1 piece on a lightly floured surface (keep the rest of the disks covered) and roll into a 5-inch circle. Line a 4-inch tart pan with a removable bottom by pressing the dough into the bottom, corners, and sides of the pan. Roll the rolling pin over the top of the pan to trim any excess. Prick the bottom of the dough with a fork. Refrigerate until ready to use. Repeat with remaining pieces of dough. Cover each prepared tart pan with foil, fill with pie weights, and place on a baking sheet. Bake shells for 18 minutes. Remove pie weights and foil and bake 10 minutes. Cool to room temperature.
- Melt butter in a large skillet over medium heat. Add shallots, leek, and onion and cook, stirring occasionally, until soft and translucent, 10 to 15 minutes. Stir in thyme. Cool to room temperature.
- Add onion mixture, eggs, cheese, cream, milk, mustard, and salt to a large bowl. Season with pepper to taste. Divide filling evenly among tart pans. Bake until the tops are golden and puffed, 25 to 30 minutes. Serve warm.