In a mixing bowl, combine flour and salt. Add cold butter and mix until the mixture resembles coarse crumbs.

Gradually add ice water, mixing until the dough comes together. Form into a ball, wrap in plastic, and refrigerate for 30 minutes.

In a frying pan over medium heat, cook the chopped onion until translucent. Add ground beef and cook until browned.

Stir in carrots, peas, Worcestershire sauce, thyme, salt, and pepper. Cook for an additional 10 minutes, then remove from heat and let cool.

Preheat the oven to 400°F (200°C). Roll out half of the pastry dough on a floured surface to fit the pie dish.

Place the rolled pastry into the pie dish, fill with the meat mixture, and cover with the remaining pastry. Seal the edges and cut slits in the top for steam to escape.

Brush the top with beaten egg for a golden finish.

Bake in the preheated oven for 30-35 minutes or until the pastry is golden brown.

Let the pie cool for a few minutes before slicing and serving.