Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add 1 cup of finely chopped onion and sauté for about 5 minutes, until they turn translucent. Then, stir in 1 tablespoon of minced garlic and 1 ½ cups of diced carrots, cooking everything together for an additional 5 minutes.

Add 1 pound of ground lamb to the skillet, and cook for about 8-10 minutes, until the lamb is thoroughly browned. Drain any excess fat.

Stir in 2 tablespoons of tomato paste and 1 tablespoon of Worcestershire sauce. Sprinkle with 1 teaspoon of fresh thyme leaves, ½ teaspoon of salt, and 1 teaspoon of black pepper. Pour in ¼ cup of beef broth and simmer for 5 to 7 minutes.

Peel and chop 2 pounds of russet potatoes, and cook in boiling salted water for 15 to 20 minutes until tender. Drain and mash with ¼ cup of butter and ¼ cup of milk. Season with salt and pepper.

Preheat your oven to 400°F (200°C). Spread the meat mixture in a baking dish and spoon the mashed potatoes on top, spreading to the edges.

Bake in the preheated oven for 20 to 25 minutes until the topping is golden brown and the filling bubbles.

Remove from the oven and let it rest for about 5 minutes before serving.