Step 1: Prepare the Oven and Cake Tins

• Preheat the oven to 180°C (356°F) or 160°C (320°F) for fan ovens.
• Grease and line 2 x 6-inch round cake tins with parchment paper.

Step 2: Make the Cake Batter

• In a large mixing bowl, cream together 225 grams of softened butter, 100 grams of caster sugar, and 125 grams of light brown sugar until pale and fluffy (about 4-5 minutes).
• Add 2 teaspoons of vanilla bean paste and 1 tablespoon of treacle; mix until combined.
• Incorporate 4 eggs one at a time, mixing well after each addition.
• Sift in 225 grams of self-raising flour and gently fold it into the batter.
• Divide the batter evenly between the prepared tins.
• Bake for 32-40 minutes or until a toothpick inserted into the center comes out clean. The cake should spring back when pressed.

Step 3: Cool and Trim the Cake Layers

• Allow the cakes to cool in the tins for 10-15 minutes, then transfer to a wire rack to cool completely.
• Once cooled, trim the tops to ensure they are flat, and slice each cake in half horizontally to create four layers.

Step 4: Prepare the Buttercream

• In a mixing bowl, beat 400 grams of softened butter using an electric whisk until very pale and fluffy (about 5 minutes).
• Gradually add 800 grams of icing sugar in three batches, mixing until fully incorporated.
• Stir in 2 teaspoons of vanilla bean paste and about 4 tablespoons of Carnation caramel. Adjust to taste.
• If the buttercream is too thick, add milk one tablespoon at a time until you reach the desired spreadable consistency.

Step 5: Assemble the Cake

• Place a small dollop of buttercream on your serving board to keep the cake in place.
• Place the first layer of cake on the board and pipe a border of buttercream around the edges.
• Inside the border, drizzle in Carnation caramel and sprinkle with flaky salt.
• Repeat layering with the remaining cake layers until you reach the top. Save the flattest layer to ensure a smooth top.
• Chill the assembled cake in the fridge for about 20 minutes to set.

Step 6: Crumb Coat and Final Frosting

• Apply a thin layer of buttercream all over the cake to seal in crumbs (known as a crumb coat).
• Chill for another 20 minutes until firm.
• Apply a thicker layer of buttercream, smoothing it with a palette knife or cake scrapper for your desired finish.

Step 7: Add the Caramel Drip

• Warm the remaining Carnation caramel in a bowl to loosen it up. Using a spoon or piping bag, drizzle it along the edges of the cake, allowing it to drip down naturally.

Step 8: Decorate and Chill

• Decorate the top with more caramel, crushed fudge pieces, or a sprinkle of flaky salt.
• Chill the finished cake for at least 30 minutes before slicing and serving.