Put the chocolate into a heatproof bowl set over a pan of shallow, gently simmering water. Stir occasionally, until melted and glossy.
Remove from the heat and stir in the rose water and sunflower oil. Set aside to cool for 2-3 minutes.
Meanwhile, line 2 baking trays with nonstick baking paper. Using a teaspoon, drop small rounds of chocolate onto the trays. When the rounds are just beginning to set, scatter over the violet crystals. Leave to set in a cool, dry place (but don’t chill).