Pre heat oven to 150°C. Grease a 5-6 cup baking dish with butter. Place Mint Slice biscuits in a food processor and process until they resemble rough crumbs. Set aside.
For the topping, combine brown sugar and cocoa in a bowl, set aside. In a separate bowl whisk flour and Mint Slice crumbs. In a jug, combine milk, butter and egg.
Pour the egg mixture into the flour mixture. Mix until combined. Spread onto the baking dish, sprinkle with sugar and cocoa mix. Gently spread out. Carefully pour the hot water over the back of a spoon over the pudding.
Place in the oven and bake for 30 minutes. Serve immediately with ice cream or cream.