Elderflower cordial

After a failed first attempt, we managed to make cordial from local Elderflowers. It tastes delicious:
30 Elderflowers
4 lemons
1kg sugar
1.5 litres boiling water
55g of citric acid

Dissolve sugar in boiled water, add citric acid. Allow to cool. Add zest of the lemons. Cut lemons into wedges and add with Elderflowers. Steep for 48 hours.