Stir 2 egg yolks, slightly beaten, and 2 tablespoons lemon juice vigorously and set aside.
Cut 1/2 cup of cold, salted butter into 8-12 chunks.
Add water to the bottom of a double boiler (don’t let it touch the top pan) and bring to a slight simmer. Add a couple chunks of butter to the top of the double boiler and let it melt.
Stir in the egg mixture and blend well with a whisk.
Continue to stir and slowly add the rest of the butter chunks.
Be sure butter melts slowly; this gives eggs time to cook and thicken sauce without curdling.
Sprinkle with a dash of paprika or cayenne pepper. Serve hot or at room temperature.
from Better Crocker’s Cookbook
Note: if you don’t have a double boiler, you can try this on direct – but extremely low – heat.
Another note: Using frozen egg yolks does NOT work!