Place mint leaves and Mint Simple Syrup in a chilled julep cup. Gently press leaves against cup with back of spoon to release flavors. Pack cup tightly with crushed ice; pour bourbon over ice. Insert straw, place mint sprig directly next to straw, and serve immediately. Sprinkle with powdered sugar, if desired.
Note: For testing purposes only, we used Woodford Reserve Distiller's Select Bourbon.
Leftover simple syrup keeps refrigerated about one week and perfectly sweetens iced tea.