My sweet Russian brought up fifteen or so blossoms from the yard Saturday afternoon, asking if that was enough... since the rest of them had "lice" on them, which he would have to pick off if I wanted more. Well... it's either make do or remove creepy inhabitants, so I cut the recipe by 1/3 to come up with this.
Pour three litres of boiling water over the blossoms in a gigantic bowl, add three kilos of sugar right away and stir like mad. (If you don't, it will lump up and sit that way until you cook it, and believe me when I say it is no easy chore getting a massive lump of sugar out of a bowl full of syrup.) Then wash thoroughly three or four lemons (if they're not organically grown you can squeeze them and use only the juice to avoid getting chemicals in your finished product), cut them up and add them, too.
Now for the fun part. For two or three days, let your mixture just sit on the counter covered by a clean towel to keep out dust and bugs. Stir every now and then. When you do that a lovely scent of elderblossom will waft up and into the kitchen, so do it often!
To finish, strain with cheesecloth and bring to a boil.
Mettre en bouteille!