Muddle the dragonfruit, mint leaves, and simple syrup in a julep cup or glass until the mint is aromatic and the dragonfruit is broken down.
Fill the glass halfway with crushed ice, then pour in the bourbon.
Stir until the outside of the glass is frosty.
Top with more crushed ice to mound it above the rim.
Garnish with a sprig of mint and a slice of dragonfruit. Serve immediately.