I have made some fondant following Rosti's recipe but it has gone rock hard straight away, can anyone tell me what I have done wrong and can it be put right?
It could also be that you were too stingy with the Glucose.
You could smash it up a bit, redissolve it and try again (with more Glucose and to a lower final temperature) - but excessive boiling could cause it to start going brown - not good for the bees.
I'd break it up as much as possible, and then "mist" it before giving it to the bees.
They'll only be able to take it slowly - especially as this is not the weather for them to go out looking for water.
"Slowly" may not be fast enough for the bees if they really need feeding.
And above an open crown board may not be the best place for the bees to access it in this cold weather. The open crown board hole in itself would be a handicap to the bees.
By all means give it to them if you have nothing better.
But if they really need fondant NOW, you ought to be trying to give them something better.
Buying a 12.5kg block from the baker is much cheaper than replacing a starved colony.