Preheat your oven to 400°F and position the rack in the middle.
This will help the quiche cook evenly from all sides.
Prepare the pie crust by thawing it and gently pricking it with a fork to prevent bubbles.
Bake it in the oven until it turns lightly golden, usually around 10 to 15 minutes.
In a skillet, heat the olive oil and add the chopped onion.
Cook until the onion softens, which should take about 3 minutes.
Add the fresh spinach to the skillet and sauté until it wilts.
This should take another 2 minutes, allowing the flavors to meld.
In a mixing bowl, whisk together the eggs, heavy cream, grated Gruyère cheese, salt, pepper, and a pinch of nutmeg.
Combine this with the spinach mixture and pour it into the pie crust.
Bake your quiche in the preheated oven for 40 to 50 minutes, or until the center is set.
Remove and let it cool slightly before slicing.