Combine pear and water in a pot, bring to a boil and cook until pears have softened and turned slightly translucent, about 6 minutes. Reduce heat to a simmer.
Add brown sugar and let simmer 30 minutes. Stir in lemon zest.
Let cool 10 minutes, then strain. Syrup can be kept in a sealed container in the refrigerator up to 5 days.
Pour rye, Carpano Antica, pear syrup, and Fernet into a mixing glass. Fill with ice. Stir until well chilled. Strain into a rocks glass filled with fresh ice.