Preheat oven to 180°C. Grease a 10-cup (2.5L) shallow ovenproof dish. Place on a baking tray.
Combine the flour, cocoa powder, hazelnut meal and combined sugar in a large bowl. Add butter and milk and stir until combined. Spoon into prepared dish and smooth the surface. Spoon over choc-hazelnut spread and use a small knife to marble.
To make the choc-hazelnut spread sauce, combine sugar and cocoa powder in a large heatproof jug. Add the water and choc-hazelnut spread and stir until combined. Pour sauce over the back of a large metal spoon onto the pudding in the dish.
Bake for 40 mins or until a skewer inserted in the centre comes out clean. Set aside for 5 mins. Dust with extra cocoa powder. Serve with ice cream.