Preheat the oven to 350ºF and prepare three 6-inch or two 8-inch cake pans by spraying the sides with cooking spray and fitting the bottoms with a wax paper or 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 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 moving on in the recipe.

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, 5-7 minutes. If you have a candy thermometer, you’ll want to cook this until it reaches 225F/107C. 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. You can either leave the container on the counter for about 2 hours or speed the cooling process slightly by placing the container in the refrigerator. It will thicken significantly as it cools.

In the bowl of a stand mixer with the paddle attachment or using a hand mixer, whip the butter on high speed until smooth and creamy, about 3 minutes. Turn the mixer to low speed and add the powdered sugar, then sift in the cocoa powder. Mix on low speed until fully combined, about 2 minutes.

Add the marshmallow creme and vanilla. Continue to mix on low speed until combined and uniform, 1-2 minutes.

In a stand mixer fitted with a paddle attachment, whip the butter on medium-high speed until creamy and light in color, 4-5 minutes.

Scrape down the bowl and paddle, then add powdered sugar, cocoa powder, milk, salt, and vanilla extract. Cover the mixer with a clean kitchen towel (to prevent ingredients flying out of the bowl), then turn the mixer to low and mix until all ingredients start to come together.

Remove the kitchen towel, scrape down the bowl and paddle, then continue mixing on low speed until uniform and smooth, 2-3 minutes.

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

Place the first layer on a turntable and pipe a circle of chocolate 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 halfway with chocolate nougat filling and smooth it down. Then, fill nearly to the top of the chocolate buttercream circle dam with thick caramel filling. Here's a detailed tutorial on this filling method in case this is your first time working with a soft filling.

Place the next cake layer on top and repeat the process of piping the chocolate buttercream circle and filling in the center with the chocolate nougat and thick caramel fillings. Place the final layer on top, upside down so that the bottom of the cake layer is the top of the cake. Crumb coat the cake with chocolate buttercream and place it in the refrigerator for at least 20 minutes to let everything set up.

To create the look pictured, frost the cake with chocolate buttercream and use an icing smoother create a semi-smooth (doesn't have to be perfect) finish. Then, hold a saw-toothed cake comb against the sides of the cake and move it slightly up and down while rotating the turntable to create the wavy buttercream texture. Place the cake into the refrigerator for 10-20 minutes to let the frosting chill while you prepare the caramel drip.

To Create the Caramel Drip: Add about ½ Cup of thick caramel filling into a microwave safe bowl and microwave in 5-10 second increments until it's slightly above room temperature and ideal drip consistency. Pour into a piping bag and snip off a small opening, then use it to pipe the caramel over the top edge of the cake, creating drips about halfway around the cake. Pipe caramel over the top of the cake in a crescent moon shape that begins and ends where the drips do, then place the cake back into the refrigerator for 5-10 minutes to let the drip set.

To finish to look, divide the remaining chocolate buttercream between two piping bags, one fitted with Wilton Tip 1M and one fitted with Wilton Tip 4B. Pipe rosettes with Tip 1M and stars with Tip 4B in a crescent formation around the top of the cake, following the caramel drip as your guide on where to begin and end. Garnish with the halved fun-size Milky Ways.