Put the squash and potatoes in two saucepans of water and bring to the boil. Cook until tender, then drain well. Lightly mash the squash with 30g butter using a fork or potato masher. Add the potatoes and continue mashing until you have a smooth puree. Season with salt and pepper then leave to cool.
Meanwhile heat a tablespoon of oil in a large deep casserole dish. When hot add the raisins and cook for a few minutes until just puffing up and changing colour. Remove with a slotted spoon and set aside.
Add another tablespoon of oil to the pan and when hot add the meat, stirring well to break up and brown all over , about 10 minutes. Add another splosh of oil then stir in the onion, carrot, celery and spices and cook for a further 10 minutes.
Stir in the raisins, tomato puree and 500 ml water and cook for another 10 minutes.
Stir the coriander throughthe mashed squash . Spoon the mince into a deep oven dish and spread the mash on top. Brush the top with a little melted butter and bake for about half an hour until the top is golden and crisp.
Remove from the oven a leave to sit for five minutes before serving.