Oil vs butter in chocolate sponge cake cake
You have attempted one of the most precise baking exercises of all... The Victorian sponge. I personally prefer to use Delia Smith's recipe. It make for a super light sponge. To make it "right" ensure that your butter and your eggs are at room temperature. My ingredients (pardon my metric) are as follows...


225 g    Butter (8 oz)
225 g    Caster Sugar (8 oz)
4 x      Medium Eggs
175 g    Self-Raising Flour (6 oz) Sieved
50 g     Cocoa Powder (2 oz)


If I deviate from this I am sure to end up with pancakes... Make sure that you sieve your flour well... It needs lots of air.

Chocolate cake on the other hand is a completely different monster.


150 g    self-raising flour, sifted
50 g     cocoa, sifted
220 g    caster sugar
80 g     butter, softened
125 ml   milk
2 x      eggs lightly beaten


Its a much heavier recipe; less SR Flour, more mechanical integration (4 minutes instead of one; more moisture in the form of milk; less eggs...