Put the flour and salt in a big bowl. Using your fingertips, work the cold, cubed butter into the flour until it resembles coarse breadcrumbs. One tablespoon of cold water at a time should be added gradually until the dough comes together.

After forming the dough into a ball, cover it tightly with plastic wrap and place it in the refrigerator for at least half an hour. The pastry is easier to roll out when chilled because it relaxes the gluten.

While the pastry chills, prepare the filling. Peel and dice the potatoes, carrots, and parsnips into small, even cubes to ensure they cook evenly.

In a large bowl, combine the ground pork, diced vegetables, chopped onion, minced garlic, fresh herbs, salt, pepper, and nutmeg. Mix gently with your hands or a spoon until just combined. Avoid overmixing, as this can make the filling dense.

Preheat your oven to 180°C (350°F).

Remove the pastry from the refrigerator and divide it into two portions, one slightly larger than the other. Roll out the larger portion and line your pie dish, allowing some overhang.

Spoon the filling into the pastry-lined dish, pressing it down gently to remove air pockets. To create the lid, roll out the remaining pastry. Place it over the filling, seal the edges, and crimp decoratively.

To let the steam out, make a tiny hole in the middle. For a golden finish, brush the top with beaten egg.

Place the pie on a baking tray and bake for 1 hour and 15 minutes, or until the pastry is deep golden brown and the filling is cooked through.

If the top browns too quickly, loosely cover it with foil during the final 15 minutes of baking.

Allow the pie to rest for at least 15 minutes before slicing.