Preheat oven to 350°F (175°C). Grease three 8-inch cake pans and line the bottoms with parchment paper.

In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.

In a separate bowl, whisk the eggs, buttermilk, oil, and vanilla. Pour into the dry ingredients and mix until just combined.

Carefully stir in the hot coffee until the batter is smooth. It will be thin. Divide evenly among the three pans.

Bake for 30-35 minutes until a toothpick comes out mostly clean. Cool in pans for 10 minutes, then transfer to a wire rack to cool completely.

For the fudge filling: Melt the chocolate chips and sweetened condensed milk in a saucepan over low heat until smooth. Stir in vanilla. Let cool at room temperature until spreadable.

For the buttercream: Beat the softened butter for 5 minutes until pale. Gradually add powdered sugar, mixing on low. Add heavy cream, peppermint extract, and salt. Whip on medium-high until fluffy.

To assemble: Level the cakes. Place one layer on a plate. Pipe a ring (dam) of buttercream around the outer edge. Spread half the cooled fudge inside the ring. Top with the second cake and repeat. Top with the final cake layer.

Frost the entire cake with a thin crumb coat of buttercream. Chill for 20 minutes. Apply the final smooth layer of buttercream and chill again.

For the drip: Heat 1/2 cup heavy cream until simmering, pour over 1/2 cup chocolate chips. Let sit 2 minutes, then stir until smooth. Let cool slightly, then drip around the edges of the chilled cake.

Garnish the top with remaining buttercream swirls, peppermint candies, and mini candy canes. Serve at room temperature.