Make the pastry by freezing the fats and flour together for 10 minutes, then tip out into the food processor and blitz to a flaky rubble. Add enough ice water to bind, then form into 2 discs, cover them with plastic wrap and rest in the refrigerator for 20 minutes.

Preheat the oven to 400°F.

Cook the pancetta or bacon in a frying pan with the onion, peppering well. Beat the green onion, parsley, and eggs together, and set aside while you roll out the pastry between plastic wrap.

Using one of the discs, line the dish, leaving an overhang. Roll out the other half between plastic wrap to make a lid, and set aside for one moment. Transfer the pancetta and onion mixture to the pastry-lined pie plate and pour over the onion, parsley, and eggs. With a little cold water, dampen the edges of the pastry shell and cover with the rolled-out lid. Cut off excess pastry, and seal and pinch all around the rim. Make a hole in the lid to let out steam, put in the oven, and bake for 30 minutes.

Sit on a wire rack until slightly above room temperature, or eat cold.