In a large bowl, combine the cubed beef with 1/2 cup flour, salt, black pepper, garlic powder, and onion powder. Toss until the beef is evenly coated.

Heat the olive oil in a large skillet over medium-high heat. Add the coated beef and sear until browned on all sides. Remove the beef from the skillet and set it aside.

In the same skillet, add the diced onion, sliced carrots, and celery. Sauté until the vegetables are softened, about 5 minutes. Add the minced garlic and cook for an additional 1 minute.

Stir in the butter until melted, then sprinkle in 1/4 cup flour. Cook for 1-2 minutes, stirring constantly. Gradually pour in the beef broth, stirring continuously to avoid lumps. Add the Worcestershire sauce and dried thyme. Bring the mixture to a simmer and cook until it thickens.

Return the seared beef to the skillet and stir to combine with the gravy. Add the frozen peas and corn kernels. Reduce the heat to low, cover, and let it simmer for 20-25 minutes, or until the beef is tender.

Preheat your oven to 375°F (190°C). Transfer the beef and vegetable mixture to a deep pie dish or baking dish. Roll out the puff pastry sheet and place it over the top of the dish, trimming any excess. Brush the pastry with the beaten egg for a golden finish.

Bake in the preheated oven for 25-30 minutes, or until the crust is golden brown and flaky. Let it cool for a few minutes before serving.