I have made elderflower jelly as the recipe says but I cannot make it set, it has now been boiled for 15mins and I am using the cold plate in the fridge method of testing, any idea's?
That recipe is for Elderflower JAM , a totally different thing to Elderflower JELLY. The pectin to make it set is in the Jam sugar which is a mix of sugar and pectin. Unless you have used jam sugar ( or added extra pectin) it will never set no matter how long it boils.