Preparation:

Step 1: Bake the Chocolate Cake Layers

1. Preheat the oven to 350°F (175°C). Grease and line three 8-inch round cake pans with parchment paper.
2. In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.
3. Add milk, vegetable oil, eggs, and vanilla extract. Beat until smooth.
4. Gradually stir in boiling water until the batter becomes thin and well-mixed.
5. Divide the batter evenly among the prepared pans.
6. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
7. Allow the cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Step 2: Prepare the Hazelnut Filling

1. In a small saucepan or microwave-safe bowl, gently heat the hazelnut spread and heavy cream until the mixture is smooth and creamy.
2. Stir in the chopped toasted hazelnuts.
3. Let the mixture cool to a spreadable consistency before using.

Step 3: Make the Chocolate Frosting

1. In a large bowl, beat the softened butter until light and creamy.
2. Gradually add the powdered sugar and cocoa powder, alternating with the heavy cream.
3. Mix in the vanilla extract. Beat until the frosting is fluffy and smooth. Adjust the consistency by adding a splash of cream if needed.

Step 4: Assemble the Cake

1. Place one cooled cake layer on a serving plate or cake stand.
2. Spread a generous amount of the hazelnut filling over the top of the cake.
3. Repeat with the second layer, spreading more hazelnut filling.
4. Place the final cake layer on top. Frost the top and sides of the cake with the chocolate frosting, smoothing it out evenly.

Step 5: Decorate the Cake

1. Drizzle the top of the cake with warmed hazelnut spread, letting it cascade down the sides.
2. Sprinkle the top with chopped toasted hazelnuts for added crunch and flavor.
3. Finish with chocolate shavings or curls for an elegant touch.