Put half of the olive oil (spray oil works just as well) into a saucepan over a medium heat and brown the mince for 7-10 minutes. Once the meat is browned remove from the pan and set to one side.
Add the remaining olive oil to the pan and turn the heat down to low. Dice the carrot, onion and celery finely. Add to the pan and cook for 5 minutes, add the garlic (garlic paste can be used if you prefer) and fry for 10 minutes, stir occasionally, until soft. Add the tomaotes, we use cherry tomatoes as they are a bit sweeter than plum tomatoes. Crumble in the stock cube, again stock pots work as well and more readily available as gluten free and add the thyme.
Tip the browned mince into the saucepan, then add the tomato puree, the worcesterhsire sauce and the water. Mix well and season to taste. Bring to the the boil then reduce to a simmer and cook for 30 minutes.
Preheat the oven to Gas mark 6. Whilst the filling is cooking make the mash for the top, feel free to change the potatoes for your choice of root veg, (Swede, Turnip or even Sweet Potato make decent alternatives). Cube the potatoes, we leave the skin on, it adds a differnet texture to the potatoes as well as keeping the nutrients and cutting down on food waste. Boil the potoatoes for 10-15 minutes until tender. Drain the potatoes and return to the heat for a few seconds stirring continuously to remove any excess water. Stir in the milk (or butter) and mash, then season to taste.
Once the meat mixture is ready, pour it into ovenproof dishes, spoon the mashed potato and spread evenly over the meaty base. Sprinkle over the cheese (or cheese alternative), put into the oven and cook for 30 minutes until golden brown.