Preheat the oven to 350ºF (177ºC) and prepare three 6-inch or two 8-inch or 9-inch cake pans by spraying the sides with baking spray and fitting the bottoms with a parchment cake circle.

Place all of the dry ingredients into the bowl of a stand mixer and stir on low for 30 seconds to fully combine them. Add the vegetable oil, eggs, vanilla, and buttermilk and mix on low until just combined. With the mixer still on low, add the hot coffee (or hot water) in a slow stream, then turn the mixer to medium and beat until smooth, about 2 minutes. The batter will be very thin.

Pour into prepared cake pans no more than ⅔ full and bake for 32-36 minutes, until a toothpick inserted comes out clean. Cool completely before assembling.

In a large saucepan over medium heat, add the sweetened condensed milk, butter, brown sugar, corn syrup, heavy whipping cream, and salt. Stir with a rubber spatula constantly until the mixture is fully combined and begins to bubble, about 5 minutes.

Continue stirring until the caramel begins to thicken, 6-7 minutes. If you have a candy thermometer, you’ll want to cook this until it reaches 225ºF (107ºC). That is the temperature that will thicken the caramel while keeping it nice and soft at room temperature.

Remove the caramel from the heat and mix in the vanilla extract. Pour into a separate container and let the caramel cool completely to room temperature before using it to fill the cake.

Place the chocolate chips into a heat resistant bowl (glass or metal) and set aside. In a saucepan over medium-high heat, warm the heavy whipping cream until it just starts to simmer. When it's reached this point, pour the cream into your bowl of chocolate, cover it with a plate, and let it sit for 2 minutes.

Whisk the chocolate and heavy cream mixture together until it’s uniform in consistency and there are no bits of chocolate left on your whisk. Cover the surface of the ganache with a piece of plastic wrap and refrigerate until the ganache is room temperature and the consistency of creamy peanut butter.

Preheat the oven to 250°F (121ºC) and line a baking sheet with parchment paper. In a medium bowl, whisk together the flour, sugar, baking powder, and salt.

Add the melted butter and vanilla extract. Mix with a rubber spatula until the mixture begins to form small clusters, then press the ingredients together with your hands to form even more clusters. Spread the clusters onto the prepared baking sheet and bake for 30 minutes. Cool the crumbs completely before using in the cake assembly.

When the caramel is cooled to room temperature, make the caramel buttercream. In a stand mixer fitted with the paddle attachment, whip the butter on high until it’s creamy and light in color, 5-6 minutes.

Add the powdered sugar and mix on low speed until combined, scraping down the bowl and paddle afterward. With the mixer still on low, mix in the vanilla extract, the caramel, salt, and 1 teaspoon of the milk. Continue mixing on low speed until fully combined.

Once the chocolate cake layers have cooled completely, level and torte each layer to your desired height. Add about 1.5 Cups of caramel buttercream into a piping bag and snip off about ½ inch opening.

Place the first cake layer on a turntable and pipe a circle of caramel buttercream around the edge of the cake layer, then pipe another circle of buttercream on top of the first to make it slightly taller. Fill in the center ⅔ of the way with the thick caramel filling and smooth it down. Then, sprinkle some shortbread crumbles on top and press them down.

Place the next cake layer on top and repeat the process of piping the caramel buttercream circle and filling in the center with the caramel and shortbread crumbles. Place the final layer on top, upside down so that the bottom of the cake layer is the top of the cake.

Mix the remaining 1-2 teaspoons of milk into the caramel buttercream to thin it out, then use it to crumb coat the cake. Place the cake into the refrigerator to firm up before adding the frosting.

When the ganache is ready to whip it will be about the consistency of smooth peanut butter. Use a stand mixer with the whisk attachment or a hand mixer, whip the ganache on medium-high speed just until it lightens in color and maintains a nice soft peak.

Immediately use the whipped chocolate to frost the cake with a smooth finish, then place the cake back into the refrigerator while you prepare the caramel for the drip.

Place the remaining caramel into a microwave safe bowl and microwave in 5-10 second intervals until it's slightly above room temperature and thick, yet pourable. Pour the caramel over the cake and use an angled spatula to push it over the edges. Sprinkle the top of the cake with the remaining shortbread crumbles.