To avoid wasting the egg yolks, use liquid egg whites. An egg white weighs 30 g and measures 2 tbsp (30 ml). Therefore, you will need ½ cup (120 g) egg whites for the cake and 1 cup (240 g) for the vanilla icing.
The mixture may separate after you add about half of the butter. Everything should come together once you add the remaining butter. This step takes time, so don’t add the butter too quickly.
If the icing seems too soft when you are ready to apply it to your cake, refrigerate it for a few minutes, then whisk it up again.
The icing can be prepared in advance if left covered at room temperature. Mix the icing well before applying it to your cake.
