Preheat the oven to 350°F.
Mix the yogurt, the melted butter (or oil), the sugar, the flour and the baking powder, the eggs and, finally the zest (or the vanilla extract or even nothing at all)
Put the preparation into a buttered and floured baking pan (preferably a metal one so the edge of the cake will be kinda crispy)
Put in the oven for 30-50 minutes or until a toothpick inserted into the center comes out clean.
Remove the cake from the pan once it has cooled down, you can either eat it like that or dust the cake with icing sugar.
