"Magic", because it creates its own sauce. And I'll give quantities for this, as they're fairly important to success!
Mix 170g self-raising flour, 90g caster sugar, 35g cocoa, 1 tsp baking powder, the grated zest of an orange and a pinch of salt in a large mixing bowl.
Whisk together the squeezed juice of the orange, 2 eggs, 70g melted butter and 100 ml whole milk, stir into the flour mixture until smooth. Add 80g
of orange milk chocolate, broken into small chunks, and tip into a buttered casserole dish. Mix 200ml boiling water with 130g light muscovado sugar
and 15g cocoa, then pour this over the pudding batter. It will look odd at this stage! Bake in a preheated 180°C oven for 30-35 minutes, until the
top is risen and crisp. Underneath the sponge will be a rich chocolate sauce. Serve with single cream (or ice cream). This will make 5 – 6 servings.