01 -
Preheat oven to 175°C. Line three 23 cm round cake tins with parchment paper. Grease pans thoroughly with nonstick spray, including the sides. Place parchment in each tin and respray to ensure complete coverage. Set aside.
02 -
In a stand mixer bowl fitted with paddle or in a large mixing bowl, combine granulated sugar, brown sugar, flour, cocoa powder, baking soda, baking powder and salt. Blend on low speed until homogeneous, breaking up any lumps by hand if necessary.
03 -
In a separate bowl, whisk eggs, egg yolks, sour cream, milk, oil, and vanilla extract until fully integrated.
04 -
Pour wet mixture into dry ingredients. Blend on low speed until just combined. With mixer running, pour in hot water and mix until evenly blended; batter will be thin.
05 -
Evenly distribute batter amongst prepared cake tins. Bake for 30 minutes or until a cake tester inserted in the centre emerges clean or with few moist crumbs. Cool cakes in tins for 10 minutes, then loosen and transfer to wire racks to cool completely.
06 -
In a stand mixer with paddle, beat softened butter on medium speed until smooth, 3 minutes. Sift icing sugar and cocoa powder into bowl. Mix on lowest speed until absorbed, then increase to medium. Add vanilla extract, salt, double cream and salted caramel sauce. Beat on medium speed for 3 minutes, adjusting consistency with more icing sugar for thickness or extra double cream as needed.
07 -
Using a serrated knife, carefully level the tops of each cooled cake layer for even assembly.
08 -
Place first layer on a serving plate or cake stand. Spread a thin layer of chocolate frosting, then drizzle with 120 ml caramel sauce. Place next cake layer on top and repeat with frosting and caramel. Place final cake layer on top.
09 -
Transfer cake to refrigerator for 1 hour to set. Once set, frost the top and sides with remaining chocolate frosting. Drizzle with additional caramel sauce and sprinkle with flaky sea salt. Slice and serve, or refrigerate for up to 5 days.