To prepare cinnamon syrup, combine sugar, 2 tablespoons water, and cinnamon in a small saucepan over medium heat. Cook 4 minutes, stirring to dissolve sugar. Remove from heat. Let stand 30 minutes; strain. Cover and keep refrigerated in a glass container for 3 to 4 weeks.
To prepare cocktail, place pear slices and 1/2 ounce cinnamon syrup in a martini shaker, and reserve the remaining cinnamon syrup for another use. Muddle pear mixture. Add ice, vodka, eau de vie, and lemon juice; shake. Strain into a cocktail glass. Garnish with additional pear slices, if desired.