Chocolate marble cake

I made this so Mike and I have something nice to take to work. Since I moved into this flat my cakes have not been rising, they usually come out quite flat. I mentioned it to mikes grandma who told me a never fail tactic for any sponge cake. Weigh the eggs in their shells, then use the same measure of butter, sugar and flour.
Sure enough, it worked! My first risen cake in 6 months!
Thanks Elsie!