Julia's Blender Hollandaise

from  Mastering the Art of French Cooking by Julia Child, Louisette Bertholle, Simone Beck
For about 3/4 cup

3 egg yolks
1/4 tsp salt
Pinch of pepper
1 to 2 Tb. lemon juice
4 oz. or 1 stick of butter

Place egg yolks, seasons, and 1 tablespoon lemon juice in the blender jar. You can beat in more lemon juice when sauce is done. That way, you will know what proportions you like for the next time.

Cut the butter into pieces and heat it to foaming hot in a small saucepan.

Cover the blender jar and blend the egg yolk mixture at top speed for 2 seconds. While still blending, start pouring on the hot butter in a thin stream of droplets (use the small opening in the lid for this, or if you don't have a lid with a small opening, you may have to partially cover the top of the jar with a towel so you don't get splashed). By the time 2/3 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. If the sauce is not used immediately, set the jar in tepid, but not warm, water.