20 elderflower heads or 50g of dried elderflowers. (This is more than most recipes, so reduce if you find the elderflower flavour a little overpowering)
You only need the florets (too much stalk can add an unwanted tannin bitterness to the brew). Remove them with a fork. Or you can buy a bag of dried elderflowers from Brewmart, where the stalks have already been removed for you.
Put them in a sterilised food grade bucket and thoroughly mix in the sugar. Leave for three hours to extract the flavour. Then add the water, and stir until the sugar has completely dissolved. next add the white grape concentrate, yeast and nutrient. Halve the lemons and squeeze, before adding the peel and stirring.
Cover the bucket, stirring occasionally for the first three or four days. After about a week, syphon into a sterilised demi-john and add an air lock. The liquor will still be sweet and still has quite a bit of fermenting to go.
This will slow down after a week or two. Test the gravity. It should read "1010". If not, then replace the air lock and leave a little longer.
Once the gravity reads 1010, syphon off into champagne-style bottles, fit fresh corks (plastic "corks" are the easiest) and the wire cages to prevent accidents.
Leave for several more weeks to allow the secondary fermentation to add some sparkle to the wine. Sediment will form and collect in the bottles during secondary fermentation. This is entirely normal. Commercial producers go to great and very complex lengths to remove sediment, whilst maintaining sparkle. At home, it is far easier to chill the bottle in the fridge then decant, carefully, into a chilled jug or decanter just before serving.