First make the pasty. Add the flour and salt to a large mixing bowl and still well. Next add the cold dripping/butter to a bowl and rub with your finger tips until the mixture resembles breadcrumbs.
Next add the egg and water and mix with a wooden spoon until the pasty comes together to form a ball. If the pastry isn't coming together, add another tablespoon of cold water.
Cover the pastry tightly with wrap and refrigerate for 30 minutes.
Meanwhile, combine the roast lamb, vegetables, gravy, herbs and pepper and stir well.
Preheat the oven to 200C/390F.
Grease the pie dish with butter or a little oil.
Once chilled, divide the pastry dough roughly into ⅔ and ⅓ portions. Take the ⅔ portion and roll to a thickness of 4mm on a lightly floured surface. Carefully transfer the rolled pastry over the base of the pie dish and press into place. Pierce the base of the pastry a few times with a fork.
Trim the pastry.
Bake the unfilled pie pasty for 10 minutes.
Add the pie filling.
Take the ⅓ portion of dough and roll to a thickness of 4mm on a lightly floured surface. Carefully transfer the pastry over the top of the filling.
Trim the pastry using a butter knife and pinch the edges of the pastry with a fork to seal. Don't worry if your pie doesn't look perfect, the more rustic the better in my opinion!
Make a small venting hole in the middle of the top of the pie.
Whisk the egg and milk to make the egg wash.
Using a pastry brush, spread the egg wash over the top of the pie.
Bake in a preheated oven at 200C/390F for 25 mins or until golden brown.