Preheat the oven to 180°C/350°F/Gas Mark 4.

In a large frying pan, heat the oil over medium heat. Add the onion and cook until soft and translucent, about 5 minutes.

Add the Beef Mince and cook until browned, breaking it up with a spoon as it cooks.

Stir in the garlic, tomato puree, and Worcestershire sauce and cook for 1-2 minutes, until fragrant.

Add the carrots, peas, beef stock, salt, and black pepper. Bring to a simmer and cook for 10-12 minutes, or until the vegetables are tender.

Transfer the beef mixture to a 22x33 cm baking dish.

Spread the mashed potatoes over the beef mixture, smoothing out the top.

Bake the shepherd's pie for 25-30 minutes, or until the mashed potatoes are lightly browned and the filling is bubbling.

Serve the shepherd's pie hot, garnished with chopped parsley, if desired.