Place mint leaves in the bottom of your julep cup or highball glass.
Add simple syrup and gently muddle the mint leaves to release their oils.
Pour in the bourbon and optional peach liqueur.
Fill the glass 3/4 full with crushed ice.
Stir the mixture with a bar spoon for 30 seconds to chill.
Top with club soda and add more crushed ice to create a mounded top.
Garnish with fresh mint sprigs and serve with a short straw.
Notes
The crushed ice is key to this drink. It should be very fine, like snow.Fresh mint makes a big difference. Choose bright green leaves without brown spots.Keep the muddling gentle - you want to release the mint oils without making the leaves bitter.The drink can be made stronger by adding an extra 1/2 oz of bourbon or lighter by using more club soda.Pre-chill the julep cup or glass in the freezer for 15 minutes before making the drink.