Step 1

Preheat oven to 400 degrees. On a floured surface, roll out dough to a 12-by-16-inch rectangle; prick all over with a fork. Whisk egg white with 1/2 teaspoon water; brush over dough. Sprinkle evenly with sesame seeds. Roll dough onto rolling pin; unroll onto a 9-by-13-inch rimmed baking sheet or shallow baking dish. Line with parchment; fill with pie weights or dry beans. Bake 20 minutes. Remove weights and parchment (if it sticks, bake a few more minutes); continue baking until golden and set on bottom, 8 to 10 minutes more (if browning too quickly, tent edges with foil). Immediately prick bottom where puffed excessively to flatten. Let cool 10 minutes.

Step 2

Scatter spinach and cheese evenly over pastry. In a large bowl, whisk together eggs, cream, 1 1/2 teaspoons salt, and 1/4 teaspoon pepper. Pour evenly over spinach and cheese. Bake until quiche is set and puffed slightly, 18 to 22 minutes (if browning too quickly, tent with foil). Let cool on a wire rack; serve warm or at room temperature.