Prepare your 3lb mold. Some molds need a wax paper liner so that you can remove the soap more easily. Make that preparation if needed.
Combine olive oil, tallow (or lard), coconut oil, and castor oil in a large pot. Melt oils and remove from burner, allowing to cool until around 90 degrees Fahrenheit.
Weigh the lye into a plastic zip close bag and set aside. Weigh the water into a plastic container and take it outside where no pets or children have access to it. Wearing gloves, a charcoal mask, and goggles, pour the lye into the water and stir until dissolved. Do not breathe out the gas made from the chemical reaction that is given off for a few minutes. Allow the lye water to cool to around 90 degrees Fahrenheit.
When lye water and oils are cooled, carefully bring the lye water inside and pour it into the oils. Using a stick blender (immersion blender), blend the soap on and off until light trace is reached. The soap will have begun to thicken where a light trace is seen when the soap is drizzled over the surface.Add essential oils and combine well.
Pour the soap into a prepared 3lb mold. Insulate with towels to keep it warm. If your house is very hot during summer months, then skip the insulation. Allow soap to sit for 24 hours. It should then be hard enough to remove from the mold. If you need to let it set for a few more hours to harden so you can get it out easier, then do so.
Cut the soap if necessary and allow to cure for 3-6 weeks. This is a hardening process where water evaporates so that the soap lasts longer when used.