Preheat the oven to 350°F

Heat the oil in a large pan until hot.
Season the ground lamb and fry in the oil over moderate to high heat for 2-3 minutes.
Stir the onions and carrot into the mince then grate the garlic in as well.
Add the Worcestershire sauce, tomato puree and herbs and cook for 1-2 minutes, stirring constantly.
Pour in the red wine and reduce until almost completely evaporated.
Add the chicken stock, bring to the boil and simmer until the sauce has thickened.  Add salt and pepper to taste.

Meanwhile, cook the potatoes in boiling salted water until tender.
Drain then return to the hot pan over low heat to dry out briefly.
Pass them through a potato ricer then beat in the egg yolks, followed by about 2 tbsp grated Parmesan.
Check for seasoning.

Spoon the lamb mixture into the bottom of a large ovenproof dish.
Using a large spoon, layer the mashed potato generously on top of the lamb mixture, starting from the outside and working your way into the middle.
Grate some extra Parmesan over and season.
Fluff up the mashed potato with a fork to make rough peaks.

Bake in the oven for approximately 20 minutes, until bubbling and golden brown.