Three-Allium Quiches | culture: the word on cheese

Ingredients

• 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)