To make the syrup, add the water and sweetener to a small saucepan and bring to the boil. Reduce to a simmer and make sure that all the sweetener is fully dissolved.

Sprinkle a pinch (no more than eighth of a teaspoon) of xanthan gum over the mixture, and quickly whisk until it too has dissolved.

Add the basil and peppercorns, and let steep for 10 minutes.

Strain the syrup and transfer it to a flip top glass bottle or similar. This recipe makes about a cup of syrup and it lasts in the fridge for up to two weeks.

To make the cocktail, add the lime and basil to a cocktail shaker and muddle them together to release as much juice and oil as possible. Add the prepared syrup and rum, and top up with ice.

Close the lid, shake well, then strain into a tall glass. Add a few ice cubes and top up with the ginger ale.