If making syrup, add the water and brown sugar to a sauce pan and heat on medium until the sugar has melted. Set aside to cool.
Add ice to a rocks glass.
Add Bourbon, banana liqueur, and brown sugar syrup. Add up to ½ ounce syrup if desired.
Finish with the black walnut and chocolate bitters and stir.
Garnish with chocolate shavings and a banana chip (optional).
