Drain the butter and simmer gently until the whey separates.
Beat the freshly squeezed orange juice with the egg yolks in a hot water bath until a firm cream forms. Season with vanilla salt. Take the pot off the stove.
Beat the butter (without whey) first drop by drop, then in a thin stream with a whisk under the cream.
Serve with asparagus and fish (e.g. tuna steaks) or roast meat and sprinkle with chervil.