Hi Heggle, you’re so lucky 
I’ve just perfected our family recipe for cordial, it makes a thick syrup and is really elderflowery
We have it well diluted with fizzy water (with or without vodka or white wine….)
30 flower heads (I know it sounds alot!) put them in a bag in the fridge overnight to make bugs sleepy so they fall off when ypu shake the heads!, 1 kg sugar, 2 lemons, 1 orange, 1.2 ltrs water, 75g citric acid (from chemist)
chop rinds off of fruit , then chop fruit and add all of it to a heat proof bowl, shake bugs from elderflower (don’t wash) and add to bowl too. In a pan add sugar and water and heat until dissolved. Pour on the elderflower and add citric acid and stir gently. Cover and leave overnight. the next day, strain and squeeze into sterilised bottles. It usually keeps quite well if sealed properly, but we never have any left past a month to know!!
you can make an elderflower tea (1 head to 1 mug) and cool and use as a toner for your skin too, it smells lovely, but doesn’t last more than a couple of days in the fridge, so it’s refreshing at least 
Enjoy your elderflower