Here, the heat of the warmed butter cooks and thickens the egg. While much easier, the blender method results in a slightly pale and less flavorful sauce. Do not make in a smaller quantity than given here—there will not be enough heat to cook the eggs properly. This may also be made with an immersion blender.

Warm a blender container by filling it with hot water and allowing it to sit for 5 minutes. Pour out the water and dry well. Add to the blender:

Melt in a small saucepan until bubbling:

Remove from the heat. Blend the egg yolks on high for 3 seconds; with the blender running, pour in the butter in a steady stream. By the time all the butter is poured in—about 30 seconds—the sauce should be finished. If not, blend on high about 5 seconds longer. If the sauce is too thick, add a few drops of warm water. Taste and adjust the seasoning with salt and lemon juice, if necessary. Serve at once or keep warm for up to 30 minutes by immersing the blender container in warm water.