Knead a soft dough from the dough ingredients. If the dough is too dry, a tablespoon of cold water may help. Chill for 30 minutes.
Roll out the dough on a clean surface until you get a thin sheet of approx. 5 mm (1/5 of an inch).
Transfer the rolled-out dough into a greased or parchment-lined tart pan or pie dish. Prick the base with a fork. You can also place parchment paper and baking weights (or dried beans) on the dough to prevent puffing.
Pre-bake the dough for 10 minutes at 180 °C/356 °F.
Remove the partially baked crust from the oven and place the spinach and chopped green onion/scallions on top.
Mix the eggs, cream, seasonings, and cheese in a bowl.
Pour the egg mixture over the spinach.
If you're using frozen spinach, it should be thawed and squeezed dry to avoid excess moisture. Fresh spinach can be lightly sauteed or wilted before adding to prevent wateriness.
Bake for 45 minutes at 180°C/356°F or until the filling has a firm consistency and a golden crust. Make sure to check at 35 minutes to prevent overcooking.
Allow to cool for 10-15 minutes before slicing and enjoy with salad or your favorite sauce.
It can be refrigerated for up to 3 days.