This recipe is adapted from Claudia Roden.  This cake has north African and Spanish roots.  According to Claudia, citrus cultivation and trade was particularly associated with Sephardi Jews around the Mediterranean, and there are any number of orange cake recipes in Sephardi culture.  

This cake is remarkable for its total lack of both butter and flour.  You could use five or so clementines or tangerines instead of the oranges. 

Don't worry if the cake sinks as it cools, or in fact turns out looking rather boring.  Trust me it is delicious, especially if served as a pudding with freshly sliced blood oranges and whipped cream.