For the basil-infused bourbon, use two full stems of basil per one liter bottle of bourbon. Start by pouring off a little bourbon to make room for the basil. Stick the herbs in the bottle and let sit for a day.
For the mint simple syrup, combine a 1:1 ratio of sugar to boiling water and then add five mint leaves per cup of syrup.
For the cocktail, muddle two medium basil leaves in a glass. Add 1.5 oz. of basil-infused bourbon and 1 oz. mint simple syrup. Add ice and soda to top, mix well. Garnish with large basil leaf.