Place mint leaves in the julep cup or rocks glass.
Add simple syrup to the glass.
Gently muddle the mint leaves with the syrup to release oils. Don't over-muddle or the mint will taste bitter.
Fill the glass halfway with crushed ice.
Pour in the bourbon.
Add more crushed ice until the glass is full.
Stir gently with a bar spoon until the glass frosts.
Top with more crushed ice to form a dome.
Garnish with a fresh mint sprig.
Notes
The quality of mint makes a big difference. Pick fresh, bright green leaves without brown spots.Store mint stems in water like flowers to keep them fresh longer.For the best results, chill the julep cup in the freezer for 10 minutes before making the drink.Using crushed ice instead of cubes helps create the signature frost on the glass exterior.Pick a bourbon between 90-100 proof for the right balance of flavor.