For garnish, unwrap the candies and place in a microwave-safe bowl. Microwave candies on high in 30 second bursts, stirring in between, until caramel is melted and smooth.
Dip the apple slice in caramel and place the dipped apple slice on a plate with parchment or wax paper. Let the apple slice chill in the fridge.
To make a cocktail, combine the bourbon, apple cider, Calvados apple brandy and vermouth in a shaker with lots of ice. Top and shake vigorously.
Strain into a chilled cocktail glass and garnish with caramel apple slice.
Notes
You can serve this cocktail on the rocks, but strain it into a glass with fresh ice. I like to use larger ice cubes for a manhattan like this.