Step 1

Preheat oven to 180C/160C fan forced. Grease a 6cm deep, 19 x 29cm baking dish with the extra butter.

Step 2

Combine the flour, 155g (3/4 cup) brown sugar and 35g (1/3 cup) cocoa powder in a large bowl. Add butter, milk, egg and vanilla and mix until well combined. Spoon into the prepared dish and spread evenly to cover the base.

Step 3

Combine the remaining cocoa powder, remaining brown sugar and 375ml (11/2 cups) boiling water in a heatproof jug. Stir to combine. Carefully pour the sauce over the back of a large metal spoon onto the pudding mixture. Bake for 25-30 minutes or until the pudding is firm to a gentle touch. Gently place 3 of the whole chocolate blocks on top of the pudding. Break the remaining chocolate block into rows and place in any gaps to fill (save any left over for later use). Bake for 2-3 minutes or until the chocolate melts slightly. Serve.