Preheat your oven to 180℃/200℃/Gas mark 6.
Heat your olive oil in a large, heavy bottomed pan. Add in the mince and fry for 5 minutes on a high heat until browned all over.
Add in the chopped vegetables and fry for a further 10 minutes until softened.
Add flour and dried herbs, stir well to coat everything, cook for a further 2-3 minutes.
Pour in beef stock, tomato puree and Worcester sauce.
Season with salt and pepper. This is personal preference but I like to add lots of both in this recipe.
Cover and simmer for 30 mins. (See notes below)
Meanwhile peel and chop your potatoes, place in cold water, and bring to the boil for 15-20 minutes, depending on the type of potato.
When the potatoes are ready, drain and mash together with the butter and plenty of salt and pepper.
Put all of your meat into a large ovenproof dish. Spread your mashed potato over the top, ruffle with a fork to give those delicious crunchy bits. (You can also sprinkle some grated cheese on top if you wish).
(At this point you can leave to cool and then freeze your pie for up to one month to get ahead with your cooking).
Bake in the oven for 25-30 minutes until the mash is browning and the mince is bubbling at the sides.
Check that it is hot inside. It may take a few minutes longer if you cooked it straight from the fridge.