My dad used to make gallons of the stuff when I was a kid. As far as I remember, it's just loads of elderflower heads in a ginormous bucket of water and enough sugar to make you puke.
plus the juice and zest of one lemon.
We try and make it every year, I can't remember excatly how much sugar (apart from a lot) but it is 40 flower heads to one gallon of water, plus sugar (about a bag) and lemon, stir, cover and leave in a bucket for 24 hours. Enjoy the aroma around the house and then bottle. They say to leave for at least 4 weeks, but I think that is a bit early and still tastes syrupy, 6 to 8 weeks is better. We use plastic lemonade bottles, but you do have to let the pressure off regularly - our last bottle had a 4 inch air gap at the top when we came to open it, it had been just about ful when made. The label had split, the bottom of the bottle was bulging out, and the bottle made a high pitched ringing sound when tapped. As the gas was released and the bottle returned to normal size the air gap just about disapeared.
Well worth the effort to make.
Edit:
This is Hugh F-W's recipie, and is basically the same as ours, except we don't bother with hot water or yeast, and the champagne definately benifits from a longer maturing period. One web site I saw said they had kept it for 2 years. I do know that the longer you keep it the more alcohol it contains. We tried one bottle after 2 weeks and it was not a patch on the later stuff.
Ingredients
About 24-30 elderflower heads, in full bloom
2kg sugar
4 litres hot water
Juice and zest of four lemons
1-2 tablespoons white wine vinegar
A pinch of dried yeast (you may not need this)
Method: How to make elderflower champagne
1. Put the hot water and sugar into a large container (a spotlessly clean bucket is good) and stir until the sugar dissolves, then top up with cold water to 6 litres.
2. Add the lemon juice and zest, the vinegar and the flower heads and stir gently.
3. Cover with clean muslin and leave to ferment in a cool, airy place for a couple of days. Take a look at the brew at this point, and if it’s not becoming a little foamy and obviously beginning to ferment, add a pinch of yeast.
4. Leave the mixture to ferment, again covered with muslin, for a further four days. Strain the liquid through a sieve lined with muslin and decant into sterilised glass bottles.
5. Seal and leave to ferment in the bottles for a further eight days before serving, chilled.