Preheat your oven to 425°F (220°C). Place one pie crust in a deep pie plate, prick with a fork, and set aside.
In a large skillet over medium-high heat, warm the light olive oil. Add the diced beef, season with kosher salt and black pepper, and cook for a few minutes until browned. Transfer the beef to a plate, keeping the juices in the pan.
In the same skillet, melt the butter. Add the chopped onions and sliced celery, cooking until soft, about 3 minutes.
Sprinkle the sautéed vegetables with flour, then slowly stir in the beef stock, whisking until thickened.
Add the milk, Worcestershire sauce, salt, and pepper. Simmer over medium-low heat until thickened, about 5 minutes. Adjust seasoning if needed.
Mix in the cooked beef and vegetables. Adjust seasoning if needed. Pour the mixture into the bottom pie crust and cover with the remaining crust.
Seal the edges and cut away excess dough. Make slits in the top crust for steam to escape. Optionally, brush the crust with beaten egg.
Bake for 35-40 minutes until the filling bubbles and the crust is golden. If the edges brown too quickly, cover with foil. Let it cool for 10 minutes before serving.
Notes
For a shiny crust, brush the top crust with an egg wash made by beating an egg with a tablespoon of water.