Heat the olive oil in a large non-stick frying pan over high heat. Add the onion and carrot and brown for 3-4 minutes.
Add the mince and fry for a further 5 minutes. Add the tomato paste, followed by the stock and rosemary. Bring up to a boil and cook for 5 minutes, then reduce to a simmer.
Season with salt and pepper to taste and simmer for a further 15-20 minutes until reduced.
Add the peas and remove the pan from the heat.
For the mash; while the potatoes are still warm, add the butter and milk and mash well. Add the grated cheese and season well with salt and freshly ground black pepper.
Spoon the meat sauce into a large oven-proof dish and top with the cheesy mashed potato - smooth over with the back of a spoon.
Top with the remaining grated cheddar cheese and pop into a preheated 200 oC oven for 8-10 minutes, until bubbling and golden.
