To make the simple syrup, combine sugar, water, lime juice, and ginger in a small saucepan. Bring to a simmer while whisking. Simmer for four minutes. Strain mixture and cool.

To make one cocktail, pour one ounce gin and one ounce simple syrup in the bottom of a glass. Stir well to combine. Add a few ice cubes. Pour in ginger ale and stir. Garnish with lime slice and a straw.