- In a bowl, combine the flour with 2 tbsp of the butter with your fingertips. Set the kneaded butter aside.
- In a saucepan, brown the pancetta, onion and garlic in the remaining butter (2 tbsp). Add the broth and potatoes. Bring to a boil. Cover and simmer for 10 minutes. Add the meat, broccoli and peas. Cook for 2 minutes. Stir in the kneaded butter. Bring back to a boil.
- Pour into a 2 litre (8-cup) capacity and 20 cm (8-inch) in diameter soufflé dish. Let cool or chill the filling completely if you want to freeze the pot pie.
- In a food processor, combine the flour and salt. Add the butter and pulse until it is the size of peas. Add the water and pulse until a ball is just beginning to form. Shape the dough into a disc. Cover with plastic wrap and refrigerate for 30 minutes.
- On a floured work surface, roll out the dough into a disc (its diameter must be 2.5 cm / 1 inch larger than the dish). With a small 2.5 cm (1-inch) cookie cutter, make a hole in the centre of the dough to allow steam to escape from the pot pie. Place the dough over filling, folding in the edge of the dough. Cut off any excess. Cover with plastic wrap. Freeze at this stage or it is ready for baking.
- With the rack in the middle position, preheat the oven to 400 °F (200 °C).
- In a small bowl, combine the egg yolk and water. Brush the dough with the egg wash.
- Bake for about 40 minutes (or 1 hour and 15 minutes if the pot pie is frozen), or until the pastry is golden brown and filling is bubbling out of the centre.