Method

• 1.
  Preheat the oven to 160°C. Grease the base and sides of two 20cm round cake pans and line with baking paper.
• 2.
  Place butter and brown sugar in a stand mixer fitted with the paddle attachment and beat until thick and pale. Add the eggs 1 at a time, beating well after each addition. Fold in soup, flour, cocoa and sour cream until completely combined.
• 3.
  Divide evenly between prepared pans and smooth using a palette knife. Bake for 1 hour 10 minutes or until a skewer inserted in the centre comes out clean. Set aside to cool completely in pans.
• 4.
  For the icing, place the chocolate in a heatproof bowl set over a saucepan of simmering water (don’t let the bowl touch the water) and stir until melted and smooth. Set aside to cool completely.
• 5.
  Place butter and icing sugar in the bowl of a stand mixer fitted with the paddle attachment and beat until thick and pale. Add the melted chocolate and beat until smooth and combined.
• 6.
  Spread 1 cake with 1 cup icing, then top with remaining cake. Cover the top and sides with a thick layer of icing, swirling to create peaks, and cut into slices to serve.