Yield: 6-inch cake (or 8-inch cake)
Preheat oven to 350 degrees F. Lightly grease three 6-inch cake rounds and line with parchment paper. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream butter. Add brown sugar and granulated sugar and mix until combined. Scrape down bowl as needed to ensure thorough mixing.
With the mixer running on low speed, add eggs one at a time. Add vanilla and mix until smooth.
In a large bowl, sift together flour, baking powder, baking soda, and cocoa powder. Whisk in espresso powder and salt. Set aside. In a large glass, combine red wine with milk. Set aside.
Add flour mixture to mixing bowl in three additions, alternating with liquids. Begin and end with flour mixture. Mix until well incorporated.
Divide batter evenly among the three prepared cake pans. Level batter using a mini offset spatula, or the back of a spoon. Bake for 35-40 minutes until a toothpick inserted in center of cake comes out clean. Let cake cool in pan for 5 minutes, then run a mini offset spatula around the cake and unmold. Let cake cool to room temperature on wire rack before assembling.
Using a hand mixer or a stand mixer fitted with a paddle attachment, cream butter. Add confectioners' sugar and salt. Mix until smooth. Add cooled melted chocolate and mix until incorporated. Increase speed and continue to mix until buttercream is fluffy.
To make soaking syrup: combine red wine and simple syrup. Set aside.
Fit a decorating bag (piping bag) with a medium round tip. Fill the bag with chocolate buttercream. Set aside.
If necessary, level cake layers. Place on cake round on cake turntable or cake stand. Using a pastry brush, lightly soak cake layer with wine syrup.
Pipe a spiral of buttercream over cake layer. Spread into an even layer with a mini offset spatula. Repeat adding wine syrup and buttercream with remaining two cake layers.
Pipe buttercream at random intervals around the cake. Use an offset spatula to create a "crumb coat" layer to seal in any crumbs. Chill cake in the fridge for 15-20 minutes to set frosting. If you don't like the "naked cake" look, add another coat of buttercream to fully cover the cake layers. Chill for another 15 minutes to set buttercream.
Spoon caramel sauce over chilled cake, allowing caramel to drip along the edges of the cake. Serve immediately.
TO MAKE SIMPLE SYRUP: combine equal parts water and sugar. Bring to a boil and let simmer until sugar has dissolved. Cool to room temperature and keep chilled until ready to use.
ABOUT CAKE SIZE: 6-inch cake rounds produces the thick cake layers photographed here. You can use 8-inch cake rounds if you would like thinner layers without altering the recipe.