Place the first chocolate cake layer on a cake board or serving plate. Pipe a ring of vanilla buttercream around the outside edge to create a dam.
Spread a layer of vanilla buttercream inside the dam, then add a layer of chocolate ganache.
Top with the next chocolate cake layer and repeat with the buttercream and ganache. Add the final cake layer on top.
Cover the entire cake with a thin crumb coat of vanilla buttercream. Chill for about 20–30 minutes, or until firm.
Frost the chilled cake with a final layer of vanilla buttercream, smoothing the sides and top as desired. Chill again until the frosting is firm.
Spoon or pour chocolate ganache over the top of the chilled cake, gently encouraging some of the ganache over the edges to create drips. Allow the ganache to set.
Dip the mini apples in the prepared thick caramel and allow the excess caramel to drip off. Place on parchment paper and let the caramel set.
Arrange the caramel apples on top of the cake. Add additional thick caramel around the apples and over the top of the cake, allowing some to naturally drip down and visually connect with the caramel apples.
Keep the finished cake chilled until shortly before serving.