Prepare and line 2 loaf pans. Hydrate the raisins in warm/hot water.Make the batter: separate the eggs. Beat the whites with a pinch of salt 5 minutes, until stiff peaks. Add the sugar in batches and mix to dissolve for another 5 minutes,Grate the zest and squeeze the orange juice. Drain the raisins. Preheat oven to 350F.In a separate bawl beat the yolks for a few minutes, then add the oil. Add the grated zest and the orange juice. Pour the yolks over the whites and incorporate them gently with a spatula.
Mix the flour with the baking powder and sift it over the batter in batches. Fold the flour slowly into the batter from bottom up. Reserve 3 tbsp of flour for later. Divide the batter and transfer 1/3 into another bawl. Add cocoa powder and mix well. To the white batter add the chopped walnuts mixed with the remaining flour. Add the raisins too. Pour the white batter into the prepared baking pans and then the cocoa batter on top.Using a fork or a butter knife make deep spirals to obtain the marble effect. Don't exaggerate.
Bake the marble loaf cakes for about 40 minutes at 350F. Remove from the oven and let them rest for 5 minutes. Remove from baking pans and transfer onto a tray to decorate and glaze.For the glaze: mix the chocolate chips with the vegetable oil and let it melt into the oven or use the bain-marie method. Pour the chocolate glaze carefully over the cakes and spread it evenly to cover all the surface.Cool completely. Let the glaze harden until next day or into the fridge. Slice and serve with a cup of coffee. Enjoy!