Wash the rosemary needles and drain well. Cut the lemon into slices.
Simmer both in 600 ml water over medium to low heat for 20 minutes. Then drain through a sieve.
Now add the sugar to the rosemary water and simmer for another 30 minutes, move the lid a little in the last 10 minutes so that the syrup can reduce a little.
Fill the syrup into sterilized jars or bottles while it is still hot.
You can mix the syrup with mineral water or sparkling wine or with gin. I like a mixture of 2 cl syrup, 2 cl gin and a shot of tonic water best.