Put the ice cubes, syrup, blackberries, vodka, grape juice and lemon juice into the blender. Blend for 15 seconds on speed 1.
Pour the cocktail through a fine sieve into a glass filled with ice cubes.
Shred 5 rose petals in the mini-grinder, for 4 pulses on speed 1 and arrange them over the cocktail.
Tips: The cane sugar syrup can be replaced with 30 ml violet syrup, a specialist syrup sold in bottles for use in cocktails, to give the drink a delicate violet flavour.