Preheat oven to 180C
Fry onion and garlic for a few minutes until tender
Add spinach, herbs, salt, pepper and water to the pan and fry until water has evaporated
Cool the filling quickly by spreading on a large plate and placing in the freezer for about 5 minutes
Once cooled, add crumbled feta cheese and egg white to the filling and mix well
Spread the mixed filling over the puff pastry sheet and roll it up
Press down the rolled pastry to flatten slightly and slice into thin pieces (approximately 11 pieces)
Mix egg yolk with 1 tsp milk and brush over the pastry slices
Sprinkle sesame seeds on top
Bake for 30-32 minutes until golden and flaky
Leave to cool for 5-10 minutes and serve warm or cool
