Put the potatoes into a pan and cover with water. Bring to the boil and simmer for 15-20 minutes until really soft.
Add the butter and cream and mash down to a lumpy but blended mash. Add the chopped herbs.
Chop the fish pieces into small chunks and add to the potato mixture. Season well.
Divide the mixture into 4 and shape into rounds about 5cm thick.
Take 3 dipped plates and put the panko breadcrumbs into one adding the spice mix of your choice and mix well.
Put the flour and egg into the remaining two plates.
Dip each fishcake into the flour, then the egg and finally coat well in the breadcrumbs.
Place on a tray. These can be frozen at this point or kept in the fridge for up to 2 days, depending on the date of your fish.
Melt the remaining butter in a frying pan and as it starts to bubble , place the fishcakes in.
Fry over a moderate heat on each side for 10-12 minutes until golden brown and crisp.
Serve with salad or peas.