This is a classic recipe and these proportions work really well.
125g (1 cup) plain, all purpose flour
a pinch of salt
120g (1/2 cup) castor sugar
3 teaspoons baking powder
4 tablespoons cocoa powder
250ml (1 cup) milk
85g (3oz) unsalted butter, melted
2 eggs lightly beaten
1 teaspoon vanilla extract
185g (1 cup) soft brown sugar
2 tablespoons cocoa powder
250 ml (1 cup) boiling water
Sift the flour, salt, sugar, baking powder and cocoa powder into a bowl.
Add the milk, butter, egg and vanilla extract and mix with beaters until combined. Pour into 4-6 greased rammekins (do NOT overfill).
To make the topping, stir the brown sugar and cocoa powder into a bowl to combine, then sprinkle it over the pudding batter. Pour boiling water carefully over the puddings.
Bake for 20-25 minutes at 180 C (350 F).