ovalette is just as same as any cake emulsifer, i think you could just substitute ovalette with other cake emulsifier. it looks like stiff egg yolk. Diana has some description about ovallete i will paste it here for you.
"Ovalette is a stabiliser used in baking sponge cakes. It helps the eggs to rise rapidly and stiffly. As it is acidic it also helps the beaten eggs to remain stable and not lose the airy and voluminous texture. It makes sponge cake softer and smoother."