Gently bruise one of the mint sprigs in the bottom of a highball glass with the Simple Syrup, then add the bourbon. Strain into a julep cup, add crushed ice until overflowing, and garnish with the remaining mint sprig.
Combine the sugar and 1 cup water in a small saucepan and bring to a boil. Cook, stirring, until the sugar dissolves. Remove from the heat and let cool completely. Keep covered in the refrigerator up to 1 month. Yield: 1 1/2 cups