Blackberry-vanilla cordial recipe | Gourmet Traveller

Ingredients

• 500 gm frozen blackberries (see note)
• Thinly peeled rind and juice of 1 orange, plus extra orange slices to serve
• 275 gm white sugar, or as required (1¼ cups)
• 1 vanilla bean, split, seeds scraped
• 2 tbsp white vinegar
• To serve: sparkling mineral water or soda water and ice cubes