To make the spiced pear syrup: In a small saucepan, combine pear juice, sugar and mulling spices. Bring to a boil, then reduce heat to a simmer. Simmer for about 30 minutes or until liquid is reduced by half. Remove from heat and cool to room temperature.
To make the cocktail: In a cocktail shaker filled with ice, combine bourbon, apple juice and syrup. Shake well. Strain into a rocks glass over ice. Garnish with fresh sage leaves.