1. Prepare Oven and Pans:

• Preheat your oven to 360°F (180°C).
• Grease and line the bottoms of two 8-inch round cake tins with parchment paper.

2. Mix Dry Ingredients:

• In a large mixing bowl, sift together the flour, cocoa powder, baking powder, and baking soda.
• Add the caster (or granulated) sugar and brown sugar. Whisk everything together until well combined.

3. Mix Wet Ingredients:

• In a separate medium mixing bowl, add the buttermilk, vegetable oil, vanilla extract, and room temperature eggs. Whisk together until combined.

4. Combine Batter:

• Add the wet ingredients to the dry ingredients in the large bowl. Begin to gently fold or mix them together with a whisk or spatula.
• Slowly pour in the hot water while continuing to mix gently until all ingredients are just incorporated and the batter is smooth. Be careful not to overmix.

5. Bake the Cake Layers:

• Divide the batter evenly between the two prepared cake tins.
• Bake for approximately 30 minutes, or until a skewer or toothpick inserted into the center comes out clean.
• Leave the cakes to cool in their tins for 10 minutes.
• Carefully remove the cakes from their tins and transfer them to wire racks to cool completely.

6. Make the Caramel Frosting:

• Ensure the butter is properly softened and the salted caramel sauce is at room temperature (stir well if separated).
• Add the softened butter to a large mixing bowl (or stand mixer bowl with paddle attachment). Beat with an electric mixer on medium-high speed until smooth and creamy.
• Gradually add the sifted powdered sugar, beating on low speed until incorporated, then increasing speed until smooth. Scrape down the bowl.
• Add the room temperature salted caramel sauce. Continue to beat on medium-high speed until the frosting is light, creamy, and well combined.

7. Assemble the Cake:

• Once the cake layers are completely cool, level the tops using a large serrated knife or cake leveler if desired (this helps create even layers).
• Place one chocolate cake layer onto your serving plate or cake stand.
• Add about half of the caramel frosting on top and spread it evenly. (Optional: Sprinkle some chopped Twix or crumbled shortbread here).
• Place the second chocolate cake layer on top.
• Frost the top and sides of the cake with the remainder of the caramel frosting, using an offset spatula to smooth it as desired.

8. Decorate:

• Generously sprinkle the top of the cake with chopped Twix bars and crumbled shortbread cookies.
• Drizzle extra salted caramel sauce over the toppings and down the sides of the cake.

9. Serve:

• Slice and serve the cake. It’s best enjoyed closer to room temperature.