Step 1Place the egg yolks, lemon juice and seasonings in the blender jar.
Step 2Cut the butter into pieces and let it heat to foaming hot in small saucepan.
Step 3Cover the jar and blend the egg yolk mixture at top speed for 2 seconds. Uncover and, still blending at top speed, immediately start pouring on the hot butter in a thin stream of droplets. (You may need to protect yourself with a towel during this operation.) By the time two-thirds of the butter has gone in, the sauce will be a thick cream. Omit the milky residue at the bottom of the butter pan. Taste the sauce, and blend in more seasonings if necessary.
Step 4If not used immediately, set the jar in tepid, but not warm, water.