Preheat your oven to 200°C/390°F/180°C fan-forced and take your puff pastry sheets out of the freezer to defrost.
Dice the onion and cut up the bacon pieces. Cook the bacon and onion until starting to brown and soften. Set aside to cool.
Grease your pie dish with butter or oil. If using a larger pie dish than you sheet of pastry cut it size and line your pie dish with pastry.
Optional: Blind bake the pastry. Cover the pastry with baking paper and pour in pie weights or something else to weigh down the pastry such as rice or dried beans. Bake in the oven for about 10 minutes. Remove and allow to cool for a few minutes, then carefully remove the baking sheet and weights.
Put four of the eggs in a bowl with the cream and Dijon mustard. Add a good grid of salt and pepper. Lightly beat until combined.
Sprinkle on the the bacon, onion and cheese. Create six small indentations in the filling and carefully crack in six eggs, taking care not to break the yolks. Pour over the egg and cream mix around the eggs, again taking care not to break the yolks.
Top the pie with pastry. Trim any excess pastry and crimp the edges with a fork. Use a small sharp knife to cut several small slits. Bake in the oven for about 35 mins or until pastry is golden brown.
To serve pop onto a plate and enjoy. Traditionally served with tomato sauce this pie is delicouls hot or cold the next day and makes great picnic food.