Pour the absinthe bitters into a rocks glass.

Swirl the absinthe around the glass to coat the inside, then discard the excess.

Place the coated glass in the freezer to chill.

Place the brown sugar cube and superfine sugar in a mixing glass.

Saturate the sugars with Peychaud's and Angostura bitters.

Muddle the sugars and bitters into a consistent paste.

Add the Rittenhouse 100-proof rye whiskey.

Stir gently.

Add large cold ice cubes to the mixing glass.

Stir for 40 revolutions.

Strain the mixture into the chilled, seasoned rocks glass.

Garnish with a lemon twist.