Heat the olive oil in a large skillet over medium heat. Add the cubed beef and cook until browned on all sides. Remove the beef from the skillet and set it aside. In the same skillet, add the onion, carrots, celery, and garlic. Cook until the vegetables are softened, about 5 minutes.

Sprinkle the flour over the vegetables and stir to coat. Slowly pour in the beef broth and grape juice, stirring constantly to avoid lumps. Add the thyme, rosemary, salt, and pepper. Return the beef to the skillet and simmer for 15-20 minutes, or until the gravy has thickened and the beef is tender.

Preheat your oven to 375°F (190°C). Divide the beef and gravy mixture evenly among four oven-safe ramekins or small baking dishes. Cut the puff pastry into circles slightly larger than the ramekins. Place a pastry circle over each ramekin, pressing the edges to seal. Brush the tops with the beaten egg for a golden finish.

Place the ramekins on a baking sheet and bake for 20-25 minutes, or until the pastry is golden brown and puffed. Let the pot pies cool for a few minutes before serving.