I'm somewhat new to making buttercream, and hadn't really developed an opinion on egg white vs egg yolk buttercreams.
Egg yolk buttercreams seem to be the most indestructible to me, and were my default for macarones because it uses up the yolks left by the egg white cookie shells.
Last weekend, I tried to make an egg white buttercream flavored with malted milk powder (replacing half the sugar in the recipe), but the cooked egg whites collapsed when I added the malted milk powder, perhaps because it does have some milk fat.
So, hounds, when do you use each type of buttercream, or does it depend on what parts of eggs you have leftover from whatever cake/cookie/pastry cream you were making?
Would my egg white buttercream have held up better if I'd cooked it to a higher temperature? Joy of Cooking said to heat to 140, which pretty much only ensures the sugar is fully incorporated, but doesn't give it the slightly cooked edge that seems to allow for a stiffer airier buttercream that is indestructible when you add fats.
I ultimately rescued the deflated but delicious malted milk egg white buttercream by making an equal sized yolk buttercream and adding back in the first one in small additions.