In a large bowl, toss the cubed beef with flour, salt, and black pepper until evenly coated.

Heat olive oil in a large skillet over medium-high heat. Add the 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, chopped celery, and minced garlic. Sauté until the vegetables are softened and fragrant, about 5 minutes.

Pour in the beef broth and grape juice, scraping the bottom of the skillet to release any browned bits. Stir in the tomato paste, dried thyme, and dried rosemary. Bring the mixture to a simmer and let it cook for 5 minutes.

Return the seared beef to the skillet and stir to combine. Reduce the heat to low, cover, and let the mixture simmer for 1 to 1.5 hours, or until the beef is tender.

Stir in the frozen peas and cook for an additional 5 minutes. Remove the skillet from heat and let the filling cool slightly.

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

Bake the pot pie 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.