The frosting will need to chill for three hours, so plan ahead by baking the chiffon cake the day before, or while the frosting is chilling.
Keep in mind though, you should never frost a warm or even lukewarm cake. It’s actually much easier to frost a chiffon cake that has been refrigerated.
Melt butter in a medium sized saucepan over medium-low heat.
Remove from heat and cool slightly.
Whisk in eggs and egg yolks, one at a time.
Return to stove on medium heat.
Bring to a low boil.
Allow to cook and bubble for 2 minutes, stirring intermittently.
In between stirring, place 2 T. cornstarch into a mesh strainer, which has been placed in a bowl.
Once the frosting has been allowed to bubble for 2 minutes, remove it from the heat.
Quickly shake the cornstarch over the frosting by tapping the strainer against the edge of the pot, while whisking the cornstarch in at the same time. This must be done
quickly and vigorously so no lumps have time to form.
Alternatively, if you have a sifter that is not hand cranked (because you need to be able to do this with one hand), you could use it instead of shaking a mesh strainer.
Pour frosting into a shallow dish and cool to room temperature.
Cover and chill for 3 or more hours until it solidifies to a frosting spreading consistency.