2 oz bourbon
1/2 oz rosemary syrup
2 dashes rhubarb bitters
Shake all ingredients over ice and pour into an ice filled highball. Top with soda water and garnish with rosemary.
To make rosemary syrup: Use a 1:1 ratio of sugar/water. One cup of sugar plus one cup of water brought to a boil and then reduced for about 5 minutes. Steep around 5 sprigs of rosemary in the hot liquid for at least 10 minutes then strain out. Let cool to room temperature and refrigerate.