Make sure you have no bugs in the flowers. Give them a good shake. Place them in a large bowl with the sliced lemon
Boil the water and pour over the flowers. Leave overnight.
Remove the sliced lemon and set aside. You'll be using the slices.
Remove the flowers and discard.
Strain the liquid through a jelly bag placed in a sieve if you have one or kitchen paper.
Place the sugar in a large saucepan. Add the liquid and the sliced lemon.
Heat slowly at first to dissolve the sugar.
Let the mixture come to the boil and boil for ten minutes.
Keep in a cool place or the fridge and use diluted in drinks and desserts. Try to use within one month.
Remember to pick your elderflowers well away from traffic or pollution.Ideally you'll need a jelly bag to strain the cordial, or use kitchen paper in a sieve. If possible, store in the fridge, it last much better.