Brush a rectangular deep ovenproof dish with butter to grease lightly.
Combine the sugar, water and golden syrup in a small saucepan. Stir over a low heat until the sugar dissolves. Then add the cocoa powder and stir until it dissolves. Remove from the heat, and leave a few minutes to cool slightly.
Place the milk and eggs in a large jug and whisk thoroughly. Add the cocoa mixture and combine well.
Place 10 bread triangles in 2 rows of 5, overlapping slightly in the baking dish. Pour a third of the cocoa mixture over the top, ensuring that all the bread is soaked with the mixture. Repeat layering with the remaining bread and cocoa to make 2 more layers. Use the back of a spoon to press the bread down to allow the cocoa mixture to soak through.
Cover and set aside at room temperature for approx 30 minutes to allow the bread to soak up the mixture.
Preheat oven to 180 degrees C. Sprinkle the pudding lightly with the extra sugar and bake for 40 minutes in the oven, until crisp on top.