Effect of flour/fat/sugar/egg ratio in a sponge pudding I thought I'd have a go at making a sponge pudding. I've Googled recipes and they all seem to be variations on creaming together fat and suger, beat in the egg then flour, then bake or steam. However different recipes vary in the ratios of flour, fat, sugar and eggs. The differences can be quite large, e.g. from one to three eggs for roughly the same amount of other ingredients.

With four ingredients there are obviously lots and lots of possible combinations, but I'm interested to know if there are any general rules for knowing what varying the amounts of ingredients will be. For example I know from experience that if you don't put in any fat you get Scotch pancakes/drop scones, which are quite elastic. Adding fat gradually changes the texture to the standard sort of Victoria sponge texture.

If this is too broad, then my main interest is that I like sponge puddings to have a coarse texture and be quite firm, so they don't turn into mush when you add the custard. I'd be interested to know how changing the amounts of the various ingredients would change the texture towards or away from this ideal.
Michael Ruhlman talks about cooking in terms of ratios in his book: Ratio: The Simple Codes Behind the Craft of Everyday Cooking.

He says the basic Sponge Cake (close cousin of Sponge Pudding) is (ratios by weight):


1 part egg
1 part sugar
1 part flour
1 part butter


And it works. This BBC recipe is along those lines.

To your Q on ratios, to make or more dense cake you could:


decrease an egg
and/or increase flour


You have other options as well. 


you could reduce leavening agents, if any
at the point you are combining butter into another ingredient, be careful not to over do it, this introduces more air into the final product.