Feta-spinach pastry

Not sure how Finnish this is, but this kind of pastries (resembling the quiche en France) are very common in Finland, and this recipe is originally from a Finnish recipe magazine. Attention, it's very filling. I served it along with onion soup yesterday, and it was an excellent combination.

Ingredients (for a mould of 24x24cm):
3-4 layers puff pastry
1 big onion
2 tablespoons oil
150 g frozen spinach
200 g feta cheese
3 eggs
2 dl light cream or cream-milk
1/4 teaspoons black pepper
a pinch of nutmeg

Preparation:
Chop the onion and sauté it on a frying pan with olive oil. Melt the spinach and squeeze the excess liquid off it. Pour the liquid off the feta cubes.
Cover the mould with puff pastry. Spread the spinach, onion and feta cheese on the puff pastry.

Mix the eggs, cream and spices together. Pour this mix on the mould.
Bake the pastry in the lower part of the 200 c hot oven for about 45 minutes.