Add the grapes, fennel syrup and rosemary to the base of a cocktail shaker and muddle to a puree. Add all other ingredients and dry shake (without ice). Open the shaker and add ice, then shake again. Fine strain into a rocks glass filled with ice, and garnish with grapes and rosemary.
* To make fennel syrup, combine a cup of sugar and half a cup of water in a small saucepan. Turn up to a medium heat and stir until the sugar is dissolved. Add half a fennel bulb (chopped) and simmer for 10 minutes. Take off the heat and leave to cool for an hour or two. Strain the syrup into an empty bottle and keep in the fridge for up to 6 weeks.