Pour all the ingredients apart from the prosecco and soda into a large wine glass and top with ice. Pour over the prosecco and finish with a splash of soda and a strawberry to garnish.
*To make the strawberry Fino: cover two cups of chopped fresh strawberries in four cups of white sugar and leave for twelve hours in a large, sealed container. After another twelve hours, pour 70cl of Fino sherry into the container with 1 vanilla pod. Leave for a further twelve hours to infuse before double-straining the resulting mix into a clean, sealable container. The Fino should keep refrigerated for three to four weeks.