foil backed plasterboard

[Robbox]

We have old stone house with thick walls and deep reveals on all the windows. In the bathroom the reveals have condensation and mould. There is actually space to bond plasterboard to these reveals, so would foil back variety help to cut down on the condensation and mould?
Thanks.

 

[Alastairreid]

To reduce the cold spot you would be looking at insulated plasterboard.

 

[Twin Dad]

Condensation will also form on the coldest surface. I would try to improve ventilation and heating and, as has been said, look at insulation.

I think that 25mm PIR board such as celotex can be used for this, if you have sufficient depth in the reveal.