Fry onion and garlic for a few minutes till tender, add in spinach, herbs, salt and pepper and the water and fry until the water has evaporated. Cool down, for quickest cooling spread on a large plate and put in the freezer, should take 5 min this way. Once cooled add in the cheese and egg white and mix well.
Preheat oven to 180C
Line the bottom of a round baking dish (it you don't have one you can use a regular rectangle one) with parchment paper
Cut your pastry into 3 equal strips lengthways
Roll out each strip gently just before you're ready to roll it up (not much or the pastry will become to thin)
Approximately divide your mixture into 3 so you know how much your working with.
Spread the mix down the pastry over to the right side leaving about 1cm from the edge, fold the pastry over as shown in the video and using your finger tuck the pastry in. Roll it over so the seal on the under side.
Once it's done roll it into a spiral as shown in the video and add to your dish. Fill the other 2 in the same and add around the first spiral starting where the previous spiral finished.
Once you've done all 3 brush with egg yolk and sprinkle sesame seeds then use a sharp serrated knife to cut into 8 the same way you'd cut a pizza.
Bake for 45-50 mins, don't be tempted to take it out of earlier even if it looks golden, hang tight for a better bake and flakey layers.