Grease a pie baking dish and unroll the store bought butter dough onto the dish. Take a fork and poke some holes in the dough. Bake it in the oven for about 10 minutes at 350℉ (with ventilator) or until it starts getting golden.
Heat 2 tbsp of olive oil in a frying pan and add finely chopped onion. Cook for a few minutes until the onion becomes soft and transparent. Set aside.
In a large bowl whisk 5 large eggs, add cream and whisk again. Squeeze out the water from the defrosted spinach and add it to the eggs together with cooked onion. Add salt and pepper and mix well.
After about 10 minutes take out the dough from the oven and pour the egg and spinach mixture. Distribute it evenly and crumble feta cheese on top. Return the pie to the oven for another 20-25 minutes or until the egg in the center of the pie is cooked.