Gather all of your equipment and ingredients.
Weigh the lard and coconut oil into a large glass bowl. Set it over a small saucepan filled with water to create a double boiler.
Boil the water until the solid fats in the bowl are melted. Remove from heat.
Meanwhile, weigh the sunflower oil into a separate bowl.
In a third large bowl, weigh the ice cubes.
In a small glass bowl or pyrex dish, weigh the lye while wearing safety glasses and gloves.
In a ventilated space, slowly sprinkle the lye into the container with the ice cubes while stirring until you have added all of the lye. Continue stirring until the lye is fully dissolved. Set aside in a safe place where it won’t get spilled.
Measure out the essential oils, if using, and set aside.
Once the solid fats have melted, combine them with the sunflower oil and stir well.
Take the temperature of the mixed oils and the temperature of the lye mixture. You will want them to be about the same temperature, in the 90-110F range. (Or that when they are combined, the average temperature will be in that range.)
Slowly pour the oils into the lye mixture and stir well with the silicone spatula.
While you are stirring, take the temperature of the oils and make sure they are within the correct range.
If so, use the immersion blender to combine the soap batter until it reaches trace.
(Trace is achieved when it is a runny pudding-like consistency and you can drizzle the batter from the blender across the surface and you can see the drizzle sit on top of the batter. Trace can be confirmed with the thermometer. It will be at least 2-3 degrees higher than it was when you first mixed the oils and lye water together.)
After you have reached trace, use the immersion blender to fully combine the essential oils if using.
Pour the batter into your soap mold.
Cover the mold with plastic wrap and set in a cool place for 48 hours or until the soap is hard enough to remove from the molds. (When making milk soaps, I refrigerate the soap in the molds during the saponification process to ensure it doesn’t overheat and turn the soap brown.)
Cut the soap into bars.
Set on a shelf to cure for 4-8 weeks. The longer you allow the soap to cure, the harder the final bar will be and the longer it will last.