Preheat the oven to 160°C (fan).
In the large mixing bowl, whisk together the light brown sugar, flour and cocoa powder. Add in the melted butter, eggs and milk and whisk until smooth.
Pour half of the batter into baking dish, top with a layer of Mint Thins (16 thins) and then spread the remaining batter over the top.
Measure the boiling water into the measuring jug and add 12 Mint Thins. Stir until the Thins have completely melted and you have a runny chocolate sauce.
Carefully pour the sauce over the surface of the batter in the baking dish then bake for 20-25 minutes until risen and springy.
Serve immediately, spooning the pudding out to reveal the sauce at the bottom and enjoy with double cream.