I made it for the first time this year - FANTASTIC!
I hunted out a thicker recipe - the reason being that I reckon the higher sugar content should keep it good for much longer - being antibacterial at this concentration. I put some in the freezer and it still didn't freeze or crystalise out the sugar so it looks stable. Here it is:-
20 Elderflower Heads
2kg Sugar
1 pt water
70g citric acid
2 lemons - rinds grated, sliced
Boil up water and sugar and citric acid. Turn off heat and chuck in the lemon and then the flower head (stalks out of the liquid if possible). Leave 12 - 18 hours under clingfilm and then strain through muslin bag. Poor into glass bottles.
Only needs about half an inch in the bottom of the glass - great with chilled water, preferably sparkling. Stir to make sure it all mixes in well.