ThisAgroposta lavender syrup is my absolute favorite and the one I used for this recipe. They ship to several countries in the EU.
A little lavender syrup goes a long way. If in doubt, rather add less than more.
I use Hendrick's gin for this recipe.
To make this cocktail for a crowd, add the blackberries, lemon juice, lavender syrup and gin to a blender or food processor. Blend until smooth and strain out the blackberry seeds if desired. Transfer the mixture into a cocktail pitcher and set it in the refrigerator to cool. Top it with sparkling water right before serving.