Cook the chestnuts for 1/2 hour in boiling water.
Remove shells and skin and put through a sieve.
Dissolve the cocoa in a Little of the milk.
Melt the margarine in a saucepan, stirring in the flour and gradually adding the milk, stirring all the time until the mixture thickens.
Cool slightly, then add the egg, the sugar, the sieved chestnuts, the dissolved cocoa and vanilla essence.
Pour into a basin or pie dish, well brushed with melted margarine, and steam for 1 1/2 hours or bake for 1 hour in a moderate oven (Regulo Mark 4). If steamed cover the pudding with greaseproof paper and a pudding cloth.
Serves 6 persons