Cream together the butter and the sugar, before gradually adding the eggs, while beating.
Carefully add the flour in small amounts along with the baking powder and salt.
Beat in the water followed by milk to get a smooth creamy consistency - adjust quantities of liquid accordingly.
In a small bowl, gently mix the fruit, 2 tbsp sugar and cornstarch. Transfer the fruit mixture to a greased pudding bowl, approximately 2 pint capacity and then spoon in the sponge mix over top and level.
Cover with double layer of waxed paper tied with string around the outside of the bowl and place in a large Dutch oven or similar pot with enough water to reach half way up the exterior of the bowl.
Simmer for 2 - 2½ hours, covered.
Serve with custard as shown if desired.