Preheat your oven to 190°C/170°C(fan)/375°F/Gas 5.
Heat 1 tablespoon Olive oil in a large heavy pan. Add 1 Onion, 2 rib Celery and 2 Carrots. Cook on a low heat for 6-7 minutes until softened.
Add 500 g Lamb mince and use a wooden spoon to separate the meat and mix well. On a gentle heat, brown the mince for 4-5 minutes.
Add 250 ml Boiling water, 1 Beef stock pot, 4 tablespoon Gravy granules, 2 tablespoon Tomato puree, 2 tablespoon Worcestershire sauce and 1 pinch Sea salt and black pepper and stir well. Cook on a low heat for 5 minutes, until thickened.
Meanwhile, make the mashed potatoes by peeling and chopping 4 Potatoes and adding to a pan of boiling water. Simmer for 15 minutes, drain and mash with the 10 g Butter and 40 g Mature cheddar.
Add the lamb mixture to a large oven proof dish and top with the mashed potatoes. Use a fork to run around the mashed potatoes, as this will help to make it nice and crispy on top.
Put it into the oven for 20 minutes.
Notes
For a richer flavour, add a splash of red wine at the same time as the stock.
If you want to make a vegan version of this, swap the lamb mince for mushrooms and lentils and make a vegan mashed potato.
For something a little different, top this shepherd's pie with sweet potato mash.
For extra flavour, add a spoonful of mint sauce at the same time as the gravy. Mint and lamb go perfectly together.
Cool the meat mixture a little before adding the potatoes. This allows it to thicken up, and also makes it easier to spread the potatoes on top. The creamier the potatoes, the easier they are to spread.