Preheat the oven to 180°C and butter a 1-litre ovenproof dish.
Sift the flour, cocoa powder, and salt into a bowl.
Cream the sugar and butter in a separate bowl until light and fluffy.
Beat in the vanilla and eggs, then fold in the flour mixture.
Mix in enough milk to reach a soft dropping consistency.
Spoon the batter into the prepared ovenproof dish.
Mix the sugar and cocoa together for the sauce and gradually beat in the milk.
Pour the sauce evenly over the uncooked cake batter.
Bake for 40 to 60 minutes until the sponge is firm to the touch.
Serve the cake hot, warm, or cold.