Elderflower Cordial & Syrup

20 elderflowers (nice big heads), gently shake off any insects & trim any excess branches/leaves
4 lemons, sliced
1.5 kg  sugar
1.8 liters water
60 gr  citric acid
Bring the sugar and water to a boil, stirring occasionally to dissolve. 
Once cooled, pour the the sugar-water and all ingredients into a big jar & cover, leave for 36-48 hours, stirring occasionally. (Some recipes say up to 3 days).
 Then remove lemons & elderflowers and strain the water a few times (if you have a cheese cloth it will help). 
Pour the syrup into a pot and cook for about 3-5 minutes minutes.
Then pour the liquid into clean sterilized glass bottles. Close them. Let them cool before placing in the refrigerator. If using a secure seal, they will keep for almost a year in the refrigerator.

To serve, pour 1-3 tablespoons of the syrup into a pint glass and add water or seltzer. Or you can add a tablespoon to a couple shots of vodka or gin.