Let’s get ready to build this amazing Twix Chocolate Layer Cake! First, prepare your oven and pans. Preheat the oven to 360°F (180°C). Grease and line the bottoms of two 8-inch round cake pans with parchment paper. Grease the parchment as well. Set aside.

Prepare the moist chocolate cake batter. In a large mixing bowl, sift together the plain (all-purpose) flour, cocoa powder, baking powder, and baking soda. Add the caster (or granulated) sugar and the packed light brown sugar. Whisk everything together thoroughly to combine and break up any lumps.

In a separate medium bowl or large measuring cup, whisk together the room temperature buttermilk, vegetable oil, vanilla extract, and room temperature eggs until well combined.

Pour the wet ingredients into the bowl containing the dry ingredients. Begin to gently fold or whisk them together. While mixing slowly, carefully pour in the hot water (or hot coffee). Continue to mix gently with a whisk or spatula just until all ingredients are incorporated and the batter is smooth. It will be a thin batter – this is correct! Do not overmix.

Divide the thin batter evenly between the two prepared cake pans. Bake for approximately 30 minutes, or until a wooden toothpick or skewer inserted into the center comes out clean. Let the cakes cool in their pans on wire racks for about 10 minutes. Then, carefully invert the cakes onto the wire racks, peel off the parchment paper, and let them cool completely before frosting.

While the cakes cool, make the Salted Caramel Frosting. Ensure your butter is properly softened to room temperature. In a large mixing bowl (using an electric mixer with paddle attachment or handheld mixer), beat the softened butter on medium-high speed until smooth, pale, and creamy – about 3-5 minutes.

Reduce the mixer speed to low. Gradually add the sifted powdered (icing) sugar, about one cup at a time, mixing until just incorporated after each addition. Once all the sugar is added, scrape down the bowl. Add the room temperature salted caramel sauce. Increase the mixer speed to medium-high and continue to beat for another 2-3 minutes until the frosting is smooth, creamy, and well combined. If it seems too stiff, you could beat in a tiny splash of milk or cream, but the caramel sauce usually provides enough liquid.

Time to assemble your Twix masterpiece! Once the cake layers are completely cool, use a long serrated knife or cake leveler to trim off any domes from the tops, creating flat surfaces. Place one cake layer, cut-side up, onto your serving plate or cake stand.

Spread about half of the salted caramel frosting evenly over the top of this first layer. Now, for maximum Twix experience (highly recommended!): sprinkle a generous amount of crumbled shortbread cookies and chopped Twix bars over this frosting layer. Gently press them in slightly.

Carefully place the second cake layer on top, preferably cut-side down for a flat top surface. Use the remaining half of the caramel frosting to cover the top and sides of the cake. Smooth it with an offset spatula as desired – a perfectly smooth finish or rustic swirls both work well for this fun cake.

Finally, decorate the top! Generously sprinkle the remaining chopped Twix bars and crumbled shortbread cookies over the top surface of the cake. Finish with an enthusiastic drizzle of extra salted caramel sauce all over the toppings. Chill the cake briefly to help the frosting set before slicing. Enjoy the ultimate Twix experience!