Sauce Mousseline (Chantilly)
The science
Whipped cream introduces a foam of air-filled fat into the emulsion, lightening the texture into something airy, mousse-like, and pale — the "mousseline" of the name. Because the cream is folded in cold and last, the sauce must be served almost immediately, before the foam deflates and the warm sauce weeps. (When made with whipped cream the sauce is also called Chantilly, after the sweetened-cream association, though here it is savory.)
Flavor profile
Hollandaise lightened by folding in whipped cream just before serving.
Culinary uses
Poached fish, asparagus, and delicate vegetables wanting an especially light, luxurious sauce.
Reference notes
Parent: Hollandaise. Technique: folding whipped cream / foams. Note the naming overlap with sweet crème Chantilly.