Take the broccoli out of the freezer about 10 minutes before starting to cook. Cut the big pieces into smaller ones (bite-size).

Preheat oven to 200 degrees C (400 degrees F). Grease well a large rectangular baking dish (optionally you can line it with baking paper).

In a bowl mix together white cheese, olive oil, melted butter and salt.

Extend two filo sheets in the baking dish, so that they cover the bottom without hanging outside. You can break them or cut them if they are too big. Arrange some of the broccoli on top and some of the white cheese filling. Sprinkle with grated yellow cheese.

Continue the same process until using all the ingredients: filo sheets, filling and grated yellow cheese. Cover with the last 2 filo sheets on top.

Lightly beat the eggs in a bowl and add the sparkling water.

Pinch the filo pie with a fork in order to create deep holes. Pour the sparkling water and egg mixture on top. Let sit for about 5 minutes so that the liquid get absorbed evenly. Bake for 30-40 minutes or until golden brown.

Let the filo pie cool for at least 30 minutes before serving it.

Keep the leftovers in airtight container in the fridge for 3-4 days. Reheat before serving.