Sweet potato-topped cottage pie

For the base: heat half of the oil in a pan, add the onion and fry until it starts to soften, then add the garlic, celery and carrot and cook until soft. Meanwhile, heat the remaining oil in a separate frying pan and fry the mince in batches, scooping each batch out with a slotted spoon and leave any excess oil behind.

Add the mince to the veg, then stir in the tomato purée and cook for 1 min. Stir in the passata and bring to a simmer. Cover and cook over a very low heat for 1½-2 hrs, then add the milk and cook for 30 mins.  If you're making the base ahead of time, you can leave it to cool at this stage then freeze for up to a month. (Defrost fully before using in the next step.)

To finish the recipe, heat more oil in a pan and fry another onion until it starts to soften. Add the carrot and celery and fry until tender. Add the thyme and bay and cook for 1 min, then tip in the mince base and bring to a simmer. Cover and cook for 20 mins (take off the lid towards the end if it’s not thick enough).

Heat oven to 180C/160C fan/gas 4. Cook the sweet potatoes in simmering water until tender, drain well, then add the milk and mash the potatoes.

Tip the meat mixture into a casserole dish and level it out (fish out the thyme and bay and discard), then pile the potato mixture on top and spread it out. Cook for 30 mins or until the top begins to brown.