In a large skillet, cook the ground beef over medium heat until browned. Drain excess fat and set the beef aside. In the same skillet, melt the butter and sauté the onion, garlic, carrots, and celery until softened, about 5 minutes.

Sprinkle the flour over the vegetables and stir to combine. Cook for 1 minute, then slowly pour in the beef broth while stirring continuously. Add the Worcestershire sauce, thyme, salt, and pepper. Bring the mixture to a simmer and cook until thickened, about 5 minutes.

Return the cooked beef to the skillet and stir in the frozen peas. Let the filling cool slightly while you prepare the pastry.

Preheat your oven to 375°F (190°C). Roll out the puff pastry and cut it into circles slightly larger than the tops of your ramekins or muffin tins. Fill each ramekin with the beef mixture, then top with a pastry circle. Press the edges to seal and brush 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 them cool for a few minutes before serving.