Preheat oven to 170°C (fan assisted).

Grease an 25 x 20cm baking dish with butter.

In a bowl, sift the muscovado sugar and cocoa powder, whisking to combine. Set aside.

In a separate bowl, sift all the dry ingredients.

In a separate bowl, whisk together the milk and butter (making sure it's no warmer than body temperature otherwise the baking powder will react too soon).

Add the egg and vanilla and whisk to combine.

Add the egg mixture to the dry ingredients and mix well to combine.

Tip in to the baking dish and even out with an off-set spatula.

Scatter the brown sugar/cocoa mixture all over the top evenly.

Spoon the boiling water carefully over the top being careful not to create craters.

Bake for 25 mins until a skewer comes out clean when poked into a spongey bit.

Cool for 10 mins then serve warm with a dollop of double cream.