Heat a large saucepan over medium-high heat until hot. Add the lamb mince, pressing it in and sear for 3 minutes. Flip and repeat on the other side.
Once seared, break it up, season with salt and pepper and continue cooking over medium heat until browned. Set the browned beef aside in a bowl.
Heat oil, then add onion, carrot, celery and garlic. Season with salt and pepper. Saute for 2-3 minutes, mixing occasionally, until softened.
Add tomato puree, saute for 2 minutes until caramelised. Deglaze the pan with the red wine, then add the worcestershire sauce and bring to a boil. Mix in the thyme and rosemary, then allow it to reduce until all the liquid is gone.
Add stock, season to taste, and cook for 1-2 minutes, then add the browned mince back in and simmer until thickened.
Meanwhile, cook the potatoes until tender (approx 10-15 minutes), then drain. Add the butter and milk to the potato pan until melted, then add the potatoes and mash. Season to taste.
Press the meat mixture into a casserole dish. Spread the mash potato on top, fork the surface, then place into a 180C oven for 20-25 minutes.
