Gather your mise en place; get together all of the equipment needed for the recipe and gather your ingredients.

In a small pot over medium heat, melt the butter.
In a 1 liter wide mouth mason jar, place the egg yolks and lemon juice.

Using the immersion blender, blend the egg yolk and lemon juice well. Slowly stream the hot butter into the mixture, being careful not to add too quickly. Incorporate all of the butter, including the milk solids.
Season with cayenne pepper and salt. Serve within 4 hours, as this sauce will set back up into butter in the refrigerator.