For the crust:
For the filling:
1. Make the pastry: In a food processor process flour, salt and cold cubed butter. Process until crumbs are formed. Add cold water, process until dough is formed. Do not over mix.
2. Transfer the dough to a work surface, pat into a ball and flatten into a disk. Wrap in plastic and refrigerate for 30 minutes.
3. Prepare spice mix: in a small bowl mix all the spices.
4. Make the filling: In a large pan or skillet heat olive oil and sauté chopped onion, celery and garlic for 4-5 minutes, until translucent. Add the meat and cook, for 4-5 minutes, until no longer pink. Season with the spice mix and stir.
5. Add the stock and bring to a boil, reduce the heat to low, simmer for 20-25 minutes, stirring occasionally, until thickness. Add the mashed potatoes to the meat mixture, stirring until thoroughly combined, cook for 3-4 minutes. remove from heat and let cool.
6. Preheat oven to 375°F/190°C
7. On a lightly floured surface, divide dough to two parts (40/60). Roll out the bigger part to about 11-12 inch (30cm) in diameter. Lay in a 8-9 inch (20-23cm) pan. Fill with cooled meat mixture. Brush around the outer edge of the pastry with the beaten egg. Roll out the second part of the pastry to about 10-11 inches (25-28cm), cut a hole in the center and place on top of the filling. Trim and then pinch the edges of the crust together and brush with the egg wash.
8. Bake for 55-60 minutes, or until golden brown. After 30 minutes add a pie crust shield or aluminum foil on top of the pie if the crust
9. Let cool for at least 1 hour before serving.