Preheat the oven to 180C / 160C Fan / Gas Mark 4. Line a 2lb loaf tin and a baking tray with non-stick parchment paper. 

On the lined baking tray, place the sweet potato and pierce it all over with a fork. Bake for 40-45 minutes or until tender.

Allow the sweet potato to cool slightly before slicing in half. Spoon the inside of the sweet potato into a large bowl and mash until smooth. Discard the potato skins. 

In a large bowl, whisk together the sugar and the vegetable oil. Add in the eggs and whisk until combined. 

In a bowl, add the Dr. Oetker Extra Dark Chocolate chips and the flour, toss until the chocolate chips are coated in flour. 

To the egg mixture, add the flour, chocolate chips, bicarbonate of soda, salt and water. Mix until just combined.

Add in the mashed sweet potatoes and stir until just mixed.

Pour the mix into the prepared loaf tin and bake for 60-65 minutes or until a skewer inserted comes out clean. 

Allow the loaf to cool for 10 minutes in the tin before transferring to a wire rack. 

Once the loaf is completely cooled, use a spoon to soften the buttercream style icing in the tub. Spoon roughly half the icing onto the top of the loaf cake and use a knife to spread the icing roughly over the cake. 

Grate the Dr. Oetker Extra Dark Chocolate onto a sheet of baking paper, then sprinkle it on top to decorate before slicing.