Heat syrup to a simmer in small saucepan. Remove from heat. Reserve 15 of the mint leaves. Add the remaining mint leaves to the syrup and let steep until cool, then strain (If you like more of a mint taste refrigerate for up to 1 week).
In a cocktail shaker, muddle the 15 reserved mint leaves with 1 part lime juice and 1 part mint maple syrup. Add ice and 1 part rum. Shake well. Fill a highball glass with ice. Pour the drink into glass. Top off with Club soda. Garnish the drink with mint sprig. Enjoy!