Preheat the oven to 350 degrees F (175 degrees C). Line the bottoms of three 8-inch cake pans with parchment paper and spray with baking spray.

Combine flour, sugar, cocoa, baking powder, baking soda, salt, and espresso powder in a large bowl and whisk until well combined. Add milk, vegetable oil, eggs, and 2 teaspoons vanilla extract to flour mixture and mix together using an electric mixer on medium speed until well combined. Reduce speed and carefully pour boiling water into cake batter. Beat on high speed for about 1 minute to add air to the batter. Distribute cake batter evenly between the prepared cake pans.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Remove from the oven and cool on a wire rack for 10 minutes. Run a table knife around the edges to loosen. Invert cakes carefully onto serving plates or cooling racks. Let cool completely. Trim tops of cakes to level, if necessary.

Place 8 ounces chopped chocolate in the heatproof bowl of a stand mixer and set aside. Whisk together 3/4 cup cream and 1 tablespoon shortening in a small saucepan and bring to a boil over medium heat. Remove from heat and pour boiling mixture over chocolate and whisk until melted and smooth. Cool to room temperature. Beat using an electric mixer on high speed until chocolate mixture is lighter in color and fluffy in texture, about 1 minute. Immediately proceed to assemble the cake before the the whipped chocolate fudge filling hardens, which makes it difficult to spread.

To assemble the cake, place 1 cooled cake layer with the trimmed side up on a cake pan or serving plate. Spread 1/2 the whipped chocolate fudge filling evenly on top. Add the next layer and spread remaining chocolate fudge filling on top. Top with third layer, trimmed side down.

To prepare the buttercream frosting, use a stand mixer affixed with the paddle attachment. Beat together butter and confectioners' sugar on low speed until well blended. Add chocolate-hazelnut spread and increase the speed to medium. Beat for 2 minutes. Add 1 teaspoon vanilla extract and kosher salt and whip for an additional 30 seconds. Add 2 tablespoons heavy whipping cream and beat until the frosting lightens slightly in color and texture, about 1 more minute.

Frost entire cake with buttercream frosting and chill for at least 1 hour.

For the chocolate drippys, place 4 ounces chopped chocolate in the heatproof bowl of a stand mixer and set aside. Whisk together 1/4 cup cream and 1/2 tablespoon shortening in a small saucepan and bring to a boil over medium heat. Pour boiling cream mixture over chocolate and whisk until melted and smooth. Let cool slightly, then pour mixture into a clean squeeze bottle. Let set until it has the consistency of thin ranch dressing. Squeeze on top of the frosted cake and allow to drip down the sides. Chill until chocolate is set. Decorate the top of the cake with assorted confections of your choice and serve at room temperature.