Preheat your oven to 375°F (190°C) and heat the vegetable oil in a large pot or Dutch oven over medium-high heat.

Add the diced lamb to the pot in batches, searing until browned on all sides, then remove the meat and set it aside.

In the same pot, add the chopped onion, potato cubes, and sliced carrots, sautéing for about 5 minutes until the onions begin to soften.

Stir in the flour and cook for 1 minute to coat the vegetables, then gradually pour in the stock while stirring constantly to prevent lumps.

Return the browned lamb to the pot along with the Worcestershire sauce and dried thyme, bringing the mixture to a simmer.

Cook gently for 30 minutes until the sauce has thickened and the vegetables are slightly tender, then remove from heat and let cool slightly.

Line a 9-inch pie dish with one sheet of the shortcrust pastry, pressing it gently into the bottom and sides.

Spoon the cooled lamb and potato filling into the pastry-lined dish, spreading it out evenly.

Place the second sheet of pastry over the top, trim the excess, crimp the edges to seal, and cut two small slits in the center for steam to escape.

Brush the top of the pastry generously with the beaten egg to ensure a golden finish.

Bake for 40 to 45 minutes until the pastry is deep golden brown and crisp.

Allow the pie to rest for 10 minutes before slicing to let the filling set, then serve warm with steamed peas or green beans.