Preheat the oven to 180C/350F/Gas 4. Butter a 1-litre (2-pint) ovenproof dish.
To make the sponge, sift the flour into a bowl with the cocoa powder and salt.
In a separate bowl, cream together the sugar and butter until light and fluffy.
Beat in the vanilla essence and the eggs then fold this mixture in the flour mixture.
Mix in just enough milk to give a soft dropping consistency.
Spoon into the buttered ovenproof dish.
For the sauce, mix the sugar and the cocoa powder together and gradually beat in the milk.
Pour evenly over the uncooked cake mixture.
Place in the oven and bake for about 40-60 minutes until firm and spongy to touch.
Serve hot, warm or cold, with or without cream.