In a large bowl beat together the two sugars and butter until smooth and creamy.
Beat in the eggs one at a time making sure they are well combined after each addition.
Sift over the flour, cocoa powder, salt and baking powder and beat until almost combined. Pour over the milk and continue mixing. Scrape down the bowl to make sure everything is incorporated.
Pour mixture into a 9 x 13-inch baking tray lined with baking paper. Place into a preheated oven at 190 C for 25-30 minutes or until a toothpick inserted comes out clean.
Leave sponge to cool slightly before poking holes all over the sponge using the end of a wooden spoon.
Ganache
For the white chocolate ganache, melt together the chocolate and cream in a microwave until smooth and well mixed. Leave to cool slightly before spreading over the cake allowing the ganache to seep into the holes. Leave to set.
Topping
Whip up the double cream to soft peaks adding icing sugar to desired sweetness.
Spread over the cooled sponge and decorate with marshmallows, chocolate shavings and caramel sauce. Enjoy :D