Melt the butter and add the sliced onion. Fry until softened.
Add the garlic and fry for a further minute or two.
Add the Worcestershire sauce and cook for one more minute.
Remove from the heat and stir in the Greek yoghurt. Leave to cool.
Pre-heat the oven to 180°C (356℉).
Roll out the dough on baking paper. You want to aim for a thin, rough, fairly large, circle.
Move the galette (along with the baking paper) on to a large baking tray.
Stir the cheese into the filling mixture.
Place the filling in the middle of the pastry circle, spreading it around evenly. Leave about 5cm around the edge of the whole circle.
Turn over the edges on to the filling, all the way around the circle, and gently press down.
Beat the egg and wash over with a brush before sprinkling with sea salt.
Bake for around 35 minutes until the pastry is nice and golden.
Remove from the oven and allow for it to cool a little before eating. Alternatively, you can dish it up cold. Enjoy!