The orange juice from a big orange is added to the beated yolks, before blending the flour, baking powder and vanilla extract. This time - because of temperature variations - the texture wasn't as spongy as the first time - as usual in my case, the first time I am trying a recipe I obtain the best results, but the taste was fresher.
You can try to have this delicious sponge cake with orange with a mint tea. Or with some hot milk with honey. We all need some extra warm during the winter season.
The source for the recipe is from Classic Kosher Cooking, by Sara Finkel, p. 216