Preheat oven to 350 F (175 C) and grease a large baking tray

In a large bowl, beat the sugar and the margarine until they are a foamy mixture

Add the eggs one at a time, then add the cornstarch, the potato starch and the salt to the egg mixture

Next add the walnuts and the chocolate; the dough should be thick at this point

Form the dough into two long oval loaves and lay them on the baking tray. Mix the remaining sugar with the cinnamon and sprinkle it on top of the loaves

Bake in the preheated oven for 50 to 55 minutes, until a toothpick comes out clean. Allow to cool and cut into slices