Preheat oven to 160C. Line a large rectangle baking pan (approx 23x33cm) with baking paper.
Melt the chocolate & nuttelex together in a microwave dish on medium power for about 2 mins. Stir to combine & set aside to cool.
Grind sugar in a thermo machine - speed 8, 8 secs. (Can use normal sugar or castor sugar if no way to grind the sugar)
Add the egg & vanilla, beat together until light & pale. (thermo machine with butterfly tool, speed 4 for 2 mins). Remove butterfly tool.
Add the flour & the melted chocolate/butter mixture, mix until combined (thermo machine speed 5, 20 secs).
Bake in the oven for 25 minutes. A light crust will from on top once cooked. Allow to cool in the pan.
Ice and decorate as desired