Melt bacon fat so that it is a liquid, but not hot. Place egg yolks and lemon juice in a stainless steel bowl and whisk until frothy. Place metal bowl over a pot of simmering water and whisk constantly until it’s ribbony and has tripled in volume. It should have a light but firm consistency. Remove from heat and very gradually add bacon fat until it is all incorporated. Taste and adjust seasoning with lemon juice, salt and pepper. It can be heated back up over a double boiler a little if needed, but don’t let it get any hotter than 140 degrees or it will break.