Place a single old fashioned glass in the freezer for 5 minutes to chill. Meanwhile, add rye whiskey, Sazerac syrup and bitters to your mixing glass.
Remove your old fashioned glass from the freezer and add the absinthe. Swirl the absinthe around the inside of the glass until the entire surface has been coated. Shake out any excess absinthe.
Add ice to your mixing glass and stir for a full 30 seconds.
Strain into your chilled old fashioned glass. Cut a small peel of lemon and delicately pinch over the top of your cocktail to release the oils. Discard the peel, or drop it into your drink for garnish.