Coarsely chop the onions and garlic.

Halve the potatoes.

Add the onions and garlic and olive oil to your slow cooker or alternatively a frying pan and cook over a low heat until brown.

Add the onions, potatoes, garlic, fish, spices and water to the slow cooker - dissolving the stock cube as you go. There is no need to defrost the fish.

Set the cooking time on your slow cooker to 4 hours, alternatively to a medium heat setting.

After 2 hours add the butter and check the water level, topping up with boiling water from the kettle if required. You may like to stir from time to time.

After 3 hours, check the liquid levels. The stock should have thickened slightly and reduced. Taste it for flavour. Season and add more boiling water if required.

Serve with a little steamed basmati rice.