Preheat the oven to 350°F (180°C).

In a skillet, heat the olive oil over medium heat, then add the diced onion, carrot, celery, potato, and minced garlic. Cook until tender, about 5-7 minutes, stirring occasionally.

Toss in the diced mushrooms along with your minced rosemary or thyme. Cook for another 3-4 minutes until the mushrooms are softened and fragrant.

In a large bowl, combine the sautéed vegetable mixture with the ground beef and thawed peas. Season with salt and pepper, thoroughly mixing everything until well combined.

On a floured surface, gently roll out the puff pastry to a rectangle.

Spoon your beef mixture onto the center of the rolled-out pastry, leaving enough space around the edges for sealing.

Fold the pastry over the filling and seal the edges tightly to prevent leaks. Brush the top generously with beaten egg.

Transfer the sealed pastry onto a baking sheet and bake for 45 minutes to 1 hour, or until it puffs up and is golden brown. Let it rest for 10 minutes before slicing.