Save a single persistent variable

I'm building a simple game in Xamarin.iOS using SpriteKit. A top score value needs to be saved permanently and updated when it's surpassed. Perhaps I'm having one of those days, but I'm not seeing a way to do it other than saving the value to a file or setting up a DB and saving it there. Both options seem overkill to me and I'd like to know if there's a way to save a variable to the app permanently with the ability to update it when needed. Can anyone shed some light, please?

Thanks.