For the filling: Heat oil in a large pot. Brown pork cubes in batches until golden. Add onions and garlic and cook until soft. Return all meat to the pot. Add stock cubes dissolved in water. Simmer for 45 minutes. Add potatoes, carrots, and herbs. Cook for 15 minutes. Add peas, mushroom soup, and cornflour mixture. Simmer for 10 minutes until thick. Cool completely.
For the pastry: Mix flour and salt in a large bowl. Rub in butter until the mixture resembles breadcrumbs. Gradually add cold water and mix to form a soft dough. Wrap and chill for 30 minutes. Roll out two-thirds for the base, line a large pie dish, and add cooled filling. Roll out the remaining pastry for the lid. Brush the edges with water and cover the pie. Crimp edges cut steam holes, and brush with beaten egg.
For the white sauce: Melt butter in a saucepan. Add flour and cook for 1 minute. Gradually add milk, stirring constantly. Add the stock cube and simmer until thick. Stir in cream and season well.
For baking: Preheat the oven to 180°C. Bake the pie for 45-50 minutes until golden brown and hot through. Let it rest for 10 minutes before serving.