The black elder was in flower last week.
That's Sambucus nigra, as opposed to the red-berried elder (Sambucus racemosa), the flowers of which aren't edible (as far as I'm aware).
Botanically, most blue and black-berried elder bushes are Sambucus nigra, these days; no more Canadian elder nor blue-berried elder.
The syrup, then. I call it syrup, cos if I were to write "Elderflower drink" everybody would think it's something alcoholic, and if I had said "Elderflower juice" most of you would have had pictures of elder flowers and a juicer in their heads.
It's easy to make:
15 of those flat elderflower bunches
1 l water (2 pints)
300 g sugar (2/3 lbs)
Remove stems from elder flowers (and yes, I'm aware that some think it barbaric to snip those flower bunches stem and all, but hey, if there's only one black elder, cos it's been planted, it'll never ever make berries - you need two elders for that); the smallest stems are OK, the larger ones aren't.
Pour water into kettle, add flowers, add the juice of two lemons, and peel and slice the third lemon (unless it's organically grown, in which case, use the peel as well).
Let sit overnight.
Strain out everything, add sugar, bring to a boil to let sugar dissolve.
Serve diluted 1:4, that is, one part elderflower syrup to 4 parts water. Dunno how long this would keep as our bush really only had the 15 flowers, and this is tasty enough in the summer heat that it's all gone in no time at all.