Start by heating the drizzled olive oil and a small pat of butter in a large pot over medium heat. Add the chopped onions and sauté until they’re soft and golden. This takes about 5-7 minutes.
Next, add the finely chopped beef skirt to the pot. Increase the heat to high. Brown the beef for about 10 minutes, stirring occasionally. The aim is to develop a nice crust on the meat.
Once the beef is browned, toss in the quartered chestnut mushrooms, rosemary, thyme, and bay leaves. The aroma will be heavenly! Cook for another 5 minutes.
Stir in the sun-dried tomato paste and aged balsamic vinegar. Now, add the stout or ale and beef broth. Bring this all to a boil.
Sprinkle in the flour and stir until mixed well. This will thicken the gravy. Let it simmer on low heat for about 30 minutes. You want the beef to become tender and soak in all the delicious flavors.
In a bowl, mix the flour, butter, and vegetarian suet until it resembles breadcrumbs. Add the mustard and salt. Gradually stir in cold water until you have a smooth dough. Wrap it in cling film and chill for 30 minutes.
Preheat your oven to 180°C (350°F). Roll out the pastry on a floured surface. Line a pie dish with half the pastry. Pour in the meat filling and top with grated cheddar.
Roll out the remaining pastry and cover the pie. Trim the edges, pinch them shut, and make a few slits in the top for steam to escape. Brush with the beaten egg for a gorgeous golden finish.
Place the pie in the oven and let it bake for 40-45 minutes. You’re looking for a puffed, golden crust.