Sauce Maltaise is a classical French derivative of hollandaise, distinguished by the substitution of lemon juice with reduced blood orange juice. The key to a stable emulsion is temperature control at every stage: the shallot reduction must be completely cool before it contacts the egg yolks, and the butter must be warm (around 60°C / 140°F) but not hot. Set a heatproof bowl over barely simmering water — the bowl base must not touch the water — and whisk the yolks and cooled reduction for 3–4 minutes until pale, thick, and ribbon-like. Add the warm butter in the thinnest possible stream, whisking constantly, almost a dribble at first until the emulsion is established. Finish with the blood orange reduction and zest. If the sauce breaks, immediately whisk in an ice cube or a splash of cold water, or rescue it by slowly whisking it into a fresh egg yolk in a clean bowl.