Wash the oranges thoroughly. Grate the peel of one into a bowl. 

Then, squeeze 100 ml of juice from them and mix it with the grated peel.

Add the baking soda to the bowl with the juice, and notice it will foam.

Measure and mix the oil and sugar in a separate bowl.

Add the juice from step 2 and the water to this mixture, and stir together.

Add the flour, and mix with a whisk to avoid lumps. You should achieve a thick cream-like dough.

Add the chopped walnuts (optional) and the fruit—here I've used black raisins, apricots, and dried currants—and mix.

Pour the batter into a 28-30cm diameter tray and bake for 35-40 minutes at 200°C.

Allow it to cool, then remove from the pan and slice as desired.

Enjoy a delightful slice.

Bon appétit!