Garnish: Lemon twist
Coat a chilled rocks glass with Absinthe (or a substitute such as Herbsaint, Pernod, ...). Pour out any excess. To a separate glass, add bitters and syrup. You can use a single sugar cube instead of simple syrup, in which case you would now muddle this to dissolve. Add to this second glass some ice, and the whiskey, and stir to chill. Strain into the first glass.