225g unsalted butter, chopped
1½ cups caster sugar
½ cup brown sugar, firmly packed
2 cups milk
1/3 cup cocoa powder
1 tsp bicarbonate of soda
4 eggs, lightly beaten
22/3 cups self-raising flour
¾ cup bottled salted caramel sauce, warmed and cooled
SALTED CARAMEL FROSTING
250g unsalted butter, chopped, at room temperature
2½ cups icing sugar mixture
¾ cup bottled salted caramel sauce
Grease two 20cm round cake pans. Line bases and sides with baking paper, extending paper 2cm above pan edges.
Combine butter, both sugars, milk and combined sifted cocoa and soda in a large saucepan. Stir over a medium heat until sugar is dissolved and butter is melted. Transfer to a large bowl. Cool mixture slightly. Add eggs and flour. Whisk until smooth. Divide evenly between prepared pans. Smooth over tops.
Cook both pans in a moderately slow oven (160C) for about 1 hour, or until cooked when tested. Stand in pans for 30 minutes. Turn out onto wire racks to cool completely.
To make salted caramel frosting, beat butter in a small bowl of an electric mixer until pale and creamy. Gradually beat in ½ cup sugar at a time, until well combined. On low speed, beat in salted caramel.
To assemble, trim tops of cakes to sit flat. Cut each cake in half horizontally.
Place one cake layer on a serving plate. Spread with ¾ cup frosting. Repeat layering with remaining cake layers and frosting, finishing with a cake layer, cut-side down. Spread remaining frosting over top.
Pour cooled salted caramel over the top, allowing it to drizzle down the side.