Swiss Buttercream
This recipe has the whites and sugar heated together before whipping.

4 cup whites
8 cup sugar
5 lbs. unsalted butter

Combine sugar and whites in the same mixing bowl you'll be whipping the eggs in. Place over a bain marie or steam table and heat until the whites are warmed through and the sugar is completely dissolved. When stirring, avoid using whipping tools or action as the incorporation of air at this stage may prevent sugar from being dissolved. Attach to mixer and wipe the outside of bowl if it has water on it. Whip stiff, then add in the butter in parts until incorporated.