Sift flour, cocoa, cornflour and salt into a bowl.
In a separate bowl, cream the butter and sugar together until light and fluffy. Add eggs one at a time, adding a tablespoon of the flour mixture with each egg. Beat until well combined. Fold in the remaining flour with the milk.
Transfer mixture to a 750ml pudding basin. Cover securely with buttered parchment or foil.
Place the basin in a pan of boiling water, cover and steam for 1 1/2 to 2 hours, or until risen and firm. (Ensure you keep checking the water level in the pan, refilling as needed, so that it doesn't boil dry.)
To serve, turn out onto a warm plate and serve with cream or custard.
I've made this loads of times and it's a really good pudding. Dead easy and quick to make and the results are always good. It's just chocolatey enough and it's a nice, light texture. Great recipe - 29 Jun 2013