First of all, on a medium low heat, heat your olive oil in your frying pan and add the onion and garlic.
Stir around for a few minutes until the onion starts to sweat and becomes translucent.
Now add your spinach leaves to the pan and increase the heat to medium. If you are using fresh spinach leaves, you might need to do this gradually, depending on the size of your pan. The leaves will soon wilt.
Mix around until all the spinach leaves have wilted and then add your salt and pepper.
Stir your salt and pepper into the spinach mixture and then turn the heat to medium high until any excess moisture evaporates.
Remove from the heat, add to a shallow bowl and allow to cool.
Now crumble your feta cheese into the spinach and gently mix it.
At this stage, start to preheat your oven to
220 °C. Take your rectangular sheets of pastry one at a time and spread a thin layer for the spinach and feta cheese mixture over the top, leaving around 1 centimetre free at the top end.
Now, carefully roll the sheets of puff pastry. Start at the bottom end and gently roll until you get to the top.
Using your sharp knife, cut each roll into four equal pieces.
Lay some greaseproof or parchment paper onto your baking tray or baking sheet.
Now take your pinwheels and place them, cut side down onto the tray, leaving a generous gap between each to make room for the pastry to puff.
Brush around and over your pinwheels with your egg wash and sprinkle the sesame seeds over the top.
Place into the centre of your preheated oven for 20 minutes and cook until your puff pastry is golden brown.
Remove from the oven and leave to cool. Serve warm or at room temperature.