How to dry out mash - added too much milk I was just making some mashed potatoes and slipped when adding milk, adding probably 50% too much.

The mash is now very liquid.  Whats the best way of saving it?

I am thinking of either heating gently to dry out a bit or adding some sort of flour to it, or both.

The mash will be used to make fishcakes if that makes a difference and has been seasoned with salt and pepper and butter.
I keep a box of instant mashed potato flakes in the house. I use it only for two things: one is a super-quick pantry chowder and the other is to thicken over milked mashed potatoes. While I wouldn't want to eat a bowl of instant mash, a quick shake in this circumstance takes care of the problem and no-one's the wiser.