Be sure to remove the puff pastry and spinach ahead of time to allow them to thaw (spinach can be quickly thawed in the microwave if needed, but do not microwave the puff pastry). Preheat your oven to 375ºF.

Dice the onion and mince the garlic. Heat the olive oil in a skillet over medium heat, then add the onion and garlic. Sauté until the onions are soft and translucent. Set aside to cool slightly.

In a bowl, combine the cottage cheese, Parmesan, nutmeg, salt, pepper, and two of the eggs, stirring until mixed well (save the third egg for brushing the pastry before baking).

Squeeze as much moisture as possible from the thawed spinach. Add the squeezed spinach, along with the sautéed onions and garlic, to the cheese mixture and stir to combine.

Place a sheet of parchment paper on your work surface (or lightly dust with flour) and roll out the thawed puff pastry until it is about 10x10 inches, just slightly larger.

Carefully drape the pastry over a pie plate. Spread the spinach and cheese mixture evenly inside the dough, then fold the corners of the pastry toward the center. The pastry will not fully cover the top, which is fine (see step-by-step photos below).

Whisk the remaining egg lightly and brush it over the surface of the pastry. Bake the spinach pie for about 45 minutes, or until the pastry has puffed up and turned golden brown.

Once baked, remove the spinach pie from the oven and let it sit for about five minutes. Slice it into eight pieces and serve.