Butter a 2 pint/1.4 litre pudding basin and put a circle of baking paper in the base of the basin.
Cut 2 of the oranges into round slices (don't use the ends), put them in a pan and cover with cold water, bring to the boil and boil for 3 minutes to blanch them. Drain on kitchen paper. Arrange in the base and around the sides of the pudding basin.
In a bowl, mix the cocoa and sugar with a little milk until smooth, then add the rest of the milk..
Zest the third orange and stir into the mixture with the orange essence, breadcrumbs, melted butter and egg yolk.
Sift the flour and bicarbonate of soda and fold into the batter.
Pour the batter into the pudding basin.
Make a lid for the pudding basin: lay out a piece of foil and top it with a piece of baking parchment, make a pleat in the middle and lay it over the pudding basin, pressing it over and around the rim.
Take a piece of string and make a slip knot, place the loop over the pudding basin and tighten. Make a handle with the string so it is easy to lift into and out of the pot.
Place the basin on an upturned saucer or trivet in a large pan half filled with water.
Bring the water to the boil then simmer with the lid on for 1 1/2 hours, checking every 30 minutes to make sure it doesn't boil dry.
Lift the basin from the pan and remove the foil lid.
Run a knife carefully around the inside of the basin and turn the pudding out onto a plate.
Serve the pudding with custard or cream and a spoonful of the orange sauce.