Ham and Cheese Slab Quiche 

Preparation

1. Step 1

   Arrange a rack in the center of your oven and set to 375 degrees. Grab two 9-by-13-inch sheet trays (no deeper than 1¼ inches), and butter the inside of one (making sure to butter the rim and lip) and underneath the second one (including the lip).

2. Step 2

   On a lightly floured surface, roll out the puff pastry until it’s wide enough to come up and slightly over the lip of a sheet tray, but by no more than ¼-inch. You’re looking for a rectangle that is roughly 12 inches wide and 15 inches long.

3. Step 3

   Transfer the puff pastry to the fully buttered sheet tray, draping it over all four lips of the pan to form a slightly hanging curtain. Gently tuck the puff pastry into the sheet tray, so it slumps into and fills the corners. Place the second sheet tray on top, securing the puff pastry. (You’re essentially inserting one baking sheet into the other, creating a puff pastry crust with four sides that will contain the filling.)

4. Step 4

   Bake for 35 minutes, until the puff pastry is lightly browned, then remove the top sheet tray and continue to bake, uncovered, for 5 to 10 minutes, until fully dry and golden brown. If the pastry starts to inflate in the middle, push it down flat after it comes out of the oven and set aside.

5. Step 5

   While the puff pastry bakes, prepare the custard: Combine the milk, cream, thyme and lemon zest in a medium pot over medium heat and cook, stirring frequently, until simmering. Turn off heat and let sit for 10 minutes, then strain it into a blender, discarding any solids. With the blender running on medium speed, add the 3 eggs all at once. Blend for 1 minute, then add the salt and black pepper. Set aside.

6. Step 6

   In a small bowl, whisk the egg yolk and Dijon mustard until no streaks of egg remain. Brush the interior bottom and sides of the puff pastry with the mustard mixture. Layer the ham evenly along the bottom of the pastry, then scatter the grated Gruyère on top in one even layer.

7. Step 7

   Strain the custard through a fine sieve into the pastry, spreading to the corners and smoothing away any bubbles from the surface with a spatula. Bake the quiche for 28 to 32 minutes, until the custard sets in the middle and the top is golden brown in spots.

8. Step 8

   Let the quiche rest for 30 minutes before slicing into slabs in the tray and serving. This can be served warm, at room temperature or even straight out of the fridge. The quiche keeps in the fridge for 3 days.