Combine ingredients in a shaker and shake vigorously without ice to start emulsion. Add ice and shake again to chill and thoroughly emulsify. Strain over ice cubes in a Collins glass and garnish with a pitted cherry on a cocktail pick and serve with a paper/metal/glass straw.
Combine cherries, water, and sugar in a medium saucepan. Bring to a boil over medium heat, stirring occasionally. Once boiling, reduce heat to medium low and simmer for 15 minutes, stirring occasionally, until the syrup is a deep ruby red and the syrup has a distinct cherry flavour.
Remove from heat and let cool to room temperature.
Store in an airtight container and refrigerate until ready to use. Cherry syrup will keep for up to two weeks in the fridge.