How to cook
In a bowl, beat the eggs with the sugar, then add the yoghurt and oil, stir well, add the flour which you've sifted with the baking powder. Stir well to obtain a medium-thick mixture (a little thicker than pancake batter).
Divide the cake batter into 2. In a cup, pour some of the mixture, add the cocoa to it and stir well.
Pour 1/2 the mixture (white part) into a buttered and floured cake form, then sprinkle with the walnuts (crushed beforehand), pour on the brown mixture, use a spoon to make stripes carefully and pour the rest of the mixture on top.
Bake in a preheated 356°F (180 °C) oven for about 30-40 min. or until reddened. Leave the ready cake to cool, invert it into a plate and sprinkle with powdered sugar and sugar sprinkles if desired.