Recreating this drink from Lucky liquor in Edinburgh using their own Sassafras liqueur. I'm sure you could use another root beer like liqueur found in the states. It was also originally made with Cutty Sark Prohibition Blend which is a great whisky for the money but as I didn't have any I decided to up the ante with some Glenfarclas 105.
2oz Cutty Sark Prohibition Blend
3/4oz lucky liquor sassafras liqueur
3/4oz banana and vanilla Demerara syrup
1/2oz coconut water
Add all ingredients to an ice filled shaker and shake vigorously. Double strain into a rocks glass or goblet over ice and enjoy.
For the syrup.
I made a 1/1 Demerara syrup on the hob, heating gently and stirring until all sugar dissolved. I then added a vanilla bean and a roughly chopped banana. Every 5 to 10 minutes I'd chop the banana into smaller pieces until completely cool then strain and bottle.