Check elderflowers for insects and dirt, don't wash them - just give them a little shake.
Add elderflowers, lemon slices and citric acid to the water in a large pan.
Boil the mixture, stirring occasionally.
Add the sugar.
Once the sugar has dissolved, remove from heat, cover and let infuse overnight.
Strain the liquid through a muslin cloth.
Sterilise some glass bottles, and the funnel as well. (don't forget about the lids!) with boiling water. If you are going to use a funnel or any other pouring aid, sterilise that, too.
Bottle the delish cordial