Place a medium stainless steel bowl or saucepan over a larger pan filled with simmering water (the bottom of the top pan should not touch the water). In the smaller top pan or bow, whisk the egg yolks with the cold water and butter. Continue whisking until the egg mixture feels warm.

Add 2 tablespoons (2 pieces) of the butter and whisk it into the egg mixture until almost fully incorporated. Repeat with remaining butter, incorporating each addition completely before adding more.

Whisk in the lemon juice and then transfer the sauce to a warm container.

If desired, add a pinch of ground cayenne pepper.

If you must keep the sauce warm, set the container in a pan of barely simmering water. If the sauce thickens too much, thin with a small amount of simmering water.