To make the raspberry puree, add the raspberries, water, and sweetener to a small saucepan. Cook over a medium heat until the fruit breaks down.

Let cool, then use a stick blender to blitz until smooth. Push the mixture through a strainer to remove any seeds. The puree can be made ahead of time then stored in the fridge.

When you're ready to make the cocktail, add the puree to a cocktail shaker, together with the remaining ingredients (apart from the garnish).

Shake until well combined, then strain into two martini glasses. Garnish with the extra fresh raspberries.