Ah - Magic Pudding. No idea about a packet version but I have a choccy one which work the same way which you have to make from scratch - but well worth it.
4 oz SR flour, marg, and sugar. 2 level tabspns cocoa (mixed with the flour) 2 eggs or 1 egg and a little milk. Cream marg and sugar, add egg(s) and a few spoons flour mix. Stir in remaining flour. Put in ovenproof dish.
Blend 3 rounded tabspns cocoa and same of sugar. Sprinkle onto uncooked pud mix. Gently pour over 3/4 pint of boiling water. Bake 35-40 mins no.4 or 180.
Just the mention of this pud on a thread on ab once got me a marriage proposal!