Very lightly muddle the fresh mint in a Mint Julep cup (or double Old-Fashioned glass).
Prepare your crushed ice in a Lewis bag, and smash with an ice hammer.
Add the simple syrup and bourbon, and fill the cup or cocktail glass halfway with crushed ice.
Stir for approximately 15 seconds with a bar spoon, until the glass frosts on the outside of your Julep cup.
Garnish with extra crushed ice, a sprig of fresh mint, and (optional) powdered sugar.