Pour all the ingredients except the soda water into a shaker and shake vigorously. Strain into a tumbler filled with ice cubes and top up with soda water. Stir gently and garnish. To make the blackberry cordial: add 250 g fresh blackberries and 125 g sugar to 100 ml water and boil for 30 minutes. Add 50 ml apple cider vinegar and stir. Then pour through a fine sieve into a bottle.