Chop the onion finely and fry it until translucent with 2 tbsp of olive oil. Clean and wash the spinach, add them to the onions and cook them for 15 minutes. When cooked whizz them and reduce them into a puree. Add salt and pepper, 2 tbsp of olive oil, egg yolks, Parmesan, chopped dill and ricotta. Stir to incorporate all the ingredients well. Grease a baking tray with some olive oil and lay on top of each other the filo pastry sheets covering all the tray. Beat the egg whites to a firm consistency and incorporate them to the ricotta mixture. Make sure you stir gently to avoid the whites going flat. Pour the mixture on the tray with the filo pastry folding the edges of the pastry inwards like a parcel. Cook in a hot oven at 180 C for 25-30 minutes until golden. Serve as soon as it comes out of the oven.