This cake is Pinkie Pie approved!
The quantities are ok for two cakes, I made a big one and a plumcake sized one. The big one was better, definitely softer.

Dry ingredients
400 grams /15 oz of 00 flour (finely milled white flour, the most common here)
250 grams /9 oz of sugar
6/7 table spoons of bitter cocoa powder
16 grams/1 oz of baking powder (I used one blister of those http://www.nifeislife.com/paneangel.....na-p-2105.html)

Soft ingredients
5 eggs, 3 yolks and 2 whole
80 grams 7 3 oz of butter (let it melt in a recipient immersed in another recipient you'll fill with water, letting it warm at a very low fire. Or in the microvawe if you own one :P)
250 grams /9 oz of white yogurt

Dressings
vanilla extract or vanillin powder (I didn't use it, and I was wrong!)
chocolate chips
hazelnuts, I used an handful of toasted hazelnuts and crumbled them with the butt of a glass. I should've used more, so try two handfuls.

I usually mix the soft ingredients, stirring util they're creamy then I add the flour. The dough can feel a bit too hard to stir, add some table spoons of water to help yourself working it. Stir until you see air bubbles appearing through the mix.
Pour a bit of the chips and hazelnut while stirring the dough, and spread the rest on the surface of the cake before putting it in the oven, so you'll avoid all of the dressing to sink to the bottom of the cake while cooking.

Bake for 30/40 minutes at 180C/356F

Nom (let it cool before) :3