Combine butter, hot water, salt, and pepper in top part of double boiler.
Blend small amount of butter mixture, about 2 teaspoons, into beaten egg yolks.
Gradually beat in remaining butter.
Place over hot, not boiling, water.
Beat with rotary beater or wire whip until thick and smooth.
Blend in lemon juice.
If sauce curdles, add 1 teaspoon hot water and blend well.