Preheat your oven to 180°C (350°F) and grease two 20cm (8-inch) cake pans, lining them with parchment paper.

In a stand mixer, cream together room temperature butter, caster sugar, and vanilla extract until light and fluffy—about 3-4 minutes.

Add eggs one at a time, mixing well after each addition.

In a separate bowl, mix Dutch processed cocoa with hot water until smooth.

Pour the cocoa mixture into the creamed butter mixture; blend until fully incorporated.

Combine vinegar with whole milk, then add alternately with sifted plain cake flour and leavening agents.

Divide the batter evenly between the prepared pans and bake for approximately 23 minutes.

Let the cakes cool in the pans for about 10 minutes before transferring to a wire rack.

Melt together caster and brown sugars in a saucepan over medium heat, stirring constantly.

Once melted, add butter and heavy cream, stirring for one minute until mixture thickens.

Sprinkle in salt flakes and allow to cool completely.

Chop dark chocolate and place in a heatproof bowl.

Heat heavy cream until just before boiling, then pour over the chocolate.

Stir until smooth and glossy, then set aside to cool slightly.

Beat softened butter on high until fluffy, about 5 minutes.

Gradually add icing sugar, mixing on low until incorporated, then increase speed.

Fold in cooled salted caramel until fully integrated.

Once cake layers are completely cooled, place one layer on a serving platter.

Spread a layer of salted caramel buttercream on top, drizzle salted caramel, and add the second layer.

Repeat the process and finish by pouring the ganache over the top.