Begin by rolling out one chilled disk of pie dough on a floured surface until you achieve a circle roughly ⅛-inch thick. Carefully roll the dough over your rolling pin and unroll it into a 9- or 9.5-inch pie dish. Gently press the dough into the base and sides of the dish using your fingertips. Trim any excess dough, ensuring there’s a ½-inch overhang. Fold the edges under to align with the rim of the pie dish, then crimp the edges using your fingers or the tines of a fork for a decorative finish. Lightly cover with plastic wrap and place in the refrigerator while the oven preheats to 425°F.

Once the oven reaches temperature, remove the crust from the fridge and prick the base several times with a fork to prevent bubbling. Line the crust with parchment paper and fill with pie weights or dried beans to hold its shape. Bake for about 15 minutes, or until the edges begin to firm up.

Carefully remove the parchment and weights, then return the crust to the oven for an additional 5 to 8 minutes, just until the bottom begins to set. Take the crust out of the oven and allow it to cool slightly.

Lower the oven temperature to 350°F.

Meanwhile, place the spinach in a steamer basket set over a pot with 1 inch of water. Bring the water to a gentle simmer, cover, and steam the spinach for 1 to 2 minutes until just wilted. Remove the spinach, let it cool briefly, then wrap it in a clean kitchen towel and squeeze out as much moisture as possible.

In a large mixing bowl, whisk together the eggs and milk until well combined. Stir in the wilted spinach, crumbled feta cheese, chopped green onions, sea salt, and a generous amount of freshly ground black pepper. Mix until evenly incorporated.

Pour the egg and spinach mixture into the partially baked crust. Use a spatula to gently spread the filling into an even layer.

Place the quiche in the oven and bake for 40 to 50 minutes, or until the center is set and no longer jiggles. Allow it to cool for about 10 minutes before slicing and serving.