For the butter cake:
1) Preheat the oven to 180C/Gas 4. Lightly butter a 32-by-22cm baking pan.
2) In a large bowl, combine the cake mix, 1 egg and 225g of the melted butter and stir until well blended. Pat the mixture into the prepared pan and set aside.
3) In a stand mixer, or with a hand mixer, beat the cream cheese until smooth. Add the remaining two eggs and the cocoa powder.
4) Lower the speed of the mixer and add the icing sugar. Continue beating until the ingredients are well mixed.
5) Slowly add the remaining 225g of melted butter and the vanilla, continuing to beat the mixture until smooth. Stir in the nuts with a rubber spatula. Spread the filling over the cake mixture in the pan.
6) Bake for 40 to 50 minutes. Be careful not to overcook the cake; the centre should still be a little gooey when finished. Allow the cake to partially cool on a wire rack.
For the ice cream:
1) Cut the ooey gooey butter cake into bite-sized pieces, adding it to the chocolate ice cream.
2) Add the crumbled biscuits and your choice of nuts.