1.Pre-heat oven 180°C/160°C (fan-forced) Grease 2 x 20cm round cake pans and line bases and sides with baking paper.
2.Place cocoa powder in a medium bowl, gradually whisk in hot water until smooth.
3.Beat butter and sugar in a large bowl with an electric mixer until light and creamy. Gradually add eggs one at a time, beating well between each addition; occasionally scrapping down sides of bowl. Gradually pour in cocoa mixture, beating until well combined.
4.Sift flour with soda, fold into butter mixture. Stir in milk. Spoon batter evenly between prepared pans, smooth over tops. Place fererro rocher chocolates over top of cakes and push down slightly.
5.Cook cakes in same oven for 1 hour and 20 minutes or until cooked; when a skewer inserted into the middle of the cake comes out clean. Stand cakes in pans for 10 minutes, before turning out onto a wire rack to cool.
6.To make ganache, stir chocolate and cream over a low heat in a large saucepan until just melted. Remove, refrigerate until a spreadable consistency.
7.Place one cake on a serving plate. Spread top with a one cup of ganache, top with other cake. Spread remaining ganache over top and side of cake.