Icing for Devil's food cake (Mary Berry). Can I use icing sugar instead of caster sugar?

You could try it with a small amount and see how it goes, but icing sugar isn’t like ordinary sugar or caster sugar and usually can’t be substituted.

The bbc recipe isn't a Mary Berry one but does use icing sugar in the icing.

www.bbcgoodfood.com/recipes/devils-food-cake?fcid=297881

Hope that helps.

Alternatively if you have granulated sugar that would be a better substitute for caster sugar though it will take longer to dissolve completely into the egg white.

I've been known to put granulated sugar into my blender to try and make caster sugar. It was fairly close.

Thank you all for your ideas - I've got the cake all made and today is icing day! I might try the blender idea with granulated sugar MiniMoon, as I've got plenty of that too.