Zest one of the oranges and set the zest aside in a small dish. Squeeze 2 tablespoons worth of juice from the zested orange (any more you can drink!). Slice the other orange, with zest still intact, into 4mm slices and cut these into half moon pieces.
For The Sponge Cake
Beat the softened butter into the sugar then gradually beat in the eggs and orange zest. Stir the spices into the flour and beat into the batter one third at a time. Finally add the vanilla extract and orange juice and beat until just smooth.