Mix together 125 g plain flour, 100 g granulated sugar, 25 g cocoa powder, 2 tsp baking powder, and ½ tsp salt
Add 60 g melted unsalted butter and 175 ml milk to the dry ingredients and stir until combined
Pour the batter into an 11 x 7 inch baking dish
In a separate bowl, combine 100 g granulated sugar, 100 g light brown sugar, and 20 g cocoa powder
Sprinkle the sugar and cocoa mixture over the batter
Pour 300 ml boiling water over the top
Bake for 35mins @ 160 degrees (fan) until the pudding is set with a soft sponge on top and a thick chocolate sauce layer underneath
Serve warm on its own or with cream, custard, or ice cream
