Step 1
To make your rhubarb syrup, cut your rhubarb into chunks and combine 500g with 500g of sugar and 500g of water. Bring to the boil stirring to dissolve the sugar. Then pull off the heat, cover with a lid and allow to cool for a few hours. When cool strain into a bottle and refrigerate, it should keep for a week.
Step 2
To make the cocktail, combine all the ingredients in a shaker with crushed ice and shake vigorously for 30 seconds until the outside is frosty. Pour the contents of the shaker into a large glass and top up with a crown of ice. Garnish with freshly shaved rhubarb.