Very easy to make Tom.
Pick the flowers early in the morning and use scissors to remove as much of the stems as possible. I use 2 litres of water to make a syrup with 3 kg of sugar. Heat it up and let it boil for a few minutes. This is for around 3-4 litres of (almost) stem-free flowers. Add the zest from 3-4 large lemons (if you can't get organically grown lemons wash them thoroughly!), remove and discard the bitter white rind-stuff from the lemons, slice them and add them to the flowers. Pour the boiling syrup over the flowers and lemons. You can add 50 grams of citric acid to help the cordial keep for longer if you like. Cover the bowl/pot (never use aluminium/aluminum containers!) and let the whole thing infuse for 3-5 days in a cool place, stir now and then to prevent mould from growing on the surface, then separate the pulp from the syrup. The pulp makes a great marmalade after a short stint in the blender. I pour the syrup into sterile bottles and it lasts for years, but you can also freeze it. I sometimes freeze it as ice cubes, which are easy to pop into cold water for a refreshing summer drink. The undiluted syrup is said to be fantastic in vodka, but I wouldn't know anything about that of course.
