Creating the Aberdeen Beef Pie is straightforward and rewarding. Follow these steps to create your masterpiece:

1. Prepare the Ingredients: Gather all ingredients and chop the vegetables as indicated.
2. Brown the Beef: In a large skillet or pot, heat the vegetable oil over medium-high heat. Add the beef cubes and brown on all sides. Remove the beef and set aside.
3. Cook the Vegetables: In the same pot, add the diced onion, carrots, and celery. Sauté until the vegetables start to soften, about 5-7 minutes.
4. Add Garlic: Stir in the minced garlic and cook for an additional minute until fragrant.
5. Combine Ingredients: Return the browned beef to the pot. Add the beef broth, tomato paste, Worcestershire sauce, thyme, rosemary, salt, and pepper. Stir to combine.
6. Thicken the Filling: Bring to a simmer and let cook for about 30 minutes, allowing the flavors to meld. If the mixture is too thin, whisk the flour with a bit of cold water to create a slurry and add it to the pot.
7. Add Peas: In the last 5 minutes of cooking, add the frozen peas, stirring them in just until heated through.
8. Preheat the Oven: While the filling cools, preheat your oven to 400°F (200°C).
9. Prepare the Pie Crust: Roll out the pie crust and fit one layer into a pie dish, letting the edges hang over.
10. Fill the Pie: Spoon the beef filling into the pie crust.
11. Top with Crust: Cover the filling with the second crust, sealing the edges by crimping them together. Cut a few slits in the top crust to allow steam to escape.
12. Brush with Egg Wash: Use the beaten egg to brush over the top of the crust for a golden finish.
13. Bake the Pie: Place the pie in the preheated oven and bake for 35-40 minutes, or until the crust is golden brown.
14. Cool Slightly: Allow the pie to cool for about 10 minutes before slicing.

By following these steps, you’ll create an Aberdeen Beef Pie that not only looks stunning but also fills your home with incredible aromas.