Mix sugar and ground cinnamon on a small plate for the rim.
Wet the rim of the martini glass with a lemon wedge, then dip in the cinnamon-sugar mixture.
Fill the cocktail shaker with ice.
Add apple vodka, cinnamon schnapps, lemon juice, and simple syrup to the shaker.
Shake hard for 10-15 seconds until well chilled.
Double strain into the prepared martini glass using both strainers.
Garnish with a thin apple slice.
Notes
The drink tastes best with fresh lemon juice rather than bottled.Store apple garnishes in cold water with a splash of lemon juice to prevent browning.For extra sweetness, use vanilla vodka instead of plain apple vodka.The cocktail can be made ahead and stored in a pitcher - just shake with ice before serving.