Rub rims of chilled martini glasses with apple slices. Place cinnamon sugar in a saucer; spin rim of each glass in cinnamon sugar. Attach one apple slice on rim of each glass.
Stir together vodka and Schnapps. Fill half of cocktail shaker with ice. Add half of vodka mixture, cover with lid, and shake 10 seconds or until thoroughly chilled. Strain into chilled glasses. Repeat with remaining vodka mixture. Serve immediately.
Note: For testing purposes only, we used DeKuyper Pucker Sour Apple Schnapps.