Method

• 1.
  Preheat oven to 160°C. Grease the base and sides of three 20cm x 7cm deep cake pans and line with baking paper.
• 2.
  Place butter, brown sugar and 3 tsp sea salt in a large saucepan over low heat and stir until smooth and combined. Whisk in caramel until smooth, then transfer to a large heatproof bowl and cool. Stir in flours and egg. Divide batter among prepared pans, tapping each pan firmly on the bench to knock out any air pockets
• 3.
  Bake mud cakes on top and bottom racks of the oven (you can leave one cake out as the other two bake, or fit two cakes on the top rack and one on the bottom) or alternatively side by side (if your oven is big enough) for 50 minutes-1 hour. Rotate cakes, then cover loosely with foil and bake for a further 50 minutes-1 hour or until a skewer inserted into the centre comes out clean. Remove cakes from oven and cool in pans for 30 minutes, then turn out onto a wire rack to cool completely. Once cooled, trim the tops from each cake so they are level, then cut each cake in half horizontally. Set aside until ready to assemble.
• 4.
  Meanwhile, for the milk chocolate ganache, place chopped chocolate in a large heatproof bowl and set aside. Place cream in a medium saucepan over medium heat. Bring to the boil, remove from the heat and pour hot cream over the chocolate, stirring continuously until the chocolate has melted and ganache is smooth. Cool for 30 minutes, then cover with plastic wrap. Set aside at room temperature for at least 1 hour or until desired consistency.
• 5.
  For the dark chocolate ganache, place chopped chocolate in a large heatproof bowl and set aside. Place cream in a medium saucepan over medium heat. Bring to the boil, remove from the heat and pour hot cream over the chocolate, stirring continuously until the chocolate has melted and ganache is smooth. Cool for 30 minutes, then cover with plastic wrap. Set aside at room temperature for at least 1 hour or until desired consistency.
• 6.
  For the caramel sauce, combine sugar and glucose with 300ml water in a medium saucepan over high heat. Bring to the boil and cook for 8-10 minutes until a golden caramel colour. Remove from the heat and gradually pour in lemon juice combined with 100ml water, taking care with the steam, whisking continuously. You should have a glassy caramel sauce. Transfer saucepan to a bowl of iced water to cool and stop the cooking process. Set aside at room temperature.
• 7.
  To assemble, place one layer of the cake on a cake stand and spread a 1cm-thick layer of milk chocolate ganache on top. If ganache is slightly soft, refrigerate until firm so the following layer of cake will not flatten the ganache layer. Top with another layer of cake and spread with a 1cm-thick layer of dark chocolate ganache. Repeat, using alternating ganache layers with each layer of cake, finishing with dark chocolate ganache on top. Place remaining milk and dark chocolate ganache in separate large piping bags each fitted with a 1cm nozzle
• 8.
  Alternating between the milk and dark chocolate ganache, pipe horizontal lines around the side of the cake until you reach the top. Using a long cranked palette knife (soak the knife in hot water to make smoothing easier) smooth over the piped ganache, taking care to not completely mix the milk and dark chocolate ganache together. Smooth the top of the cake so ganache meets at a neat right angle around the edge. Refrigerate for 10-15 minutes to set.
• 9.
  To serve, top with salted caramel popcorn and drizzle over caramel sauce. Serve immediately. This cake is best served at room temperature – if you refrigerate for too long, it will become very firm.