Okay, you win, Alan, orange sponge cake DOES exist
...
Maybe those long-haired 'lassies' in the Clachaig will bake one for you
Ingredients: 3 eggs, separated; 200g (7 oz) caster sugar; 1 tablespoon orange zest; 200g (7 oz) plain flour; 1 dessertspoon baking powder; and 6 tablespoons orange juice.
Preparation method: 1. Preheat oven to 160 C / Gas mark 3. Grease and flour one 23cm (9 in) cake tin.
2. Beat egg yolks, sugar and orange zest until light and fluffy. Mix flour and baking powder together. Alternately add flour mixture and orange juice to the egg yolk mixture.
3. In a separate large clean bowl, with a clean wire whisk or electric beater, beat egg whites to stiff peaks, and fold into batter.
4. Pour batter into prepared tin and bake in preheated oven for 50 to 60 minutes.