Put on safety goggles, gloves, and long sleeves. Work in a well-ventilated room with kids and pets out of the way, and use stainless steel, glass, or heatproof plastic, never aluminum.

Weigh the distilled water into a heatproof container. Slowly pour the lye into the water (never water into lye), stirring until it dissolves. Don’t breathe the fumes.

Set the lye solution aside to cool to about 120 to 130°F. This can take an hour or more.

Melt the coconut oil and combine it with the olive and sweet almond oil in a large stainless steel or glass bowl. Bring the oils to about the same temperature as the lye solution, within 10 degrees or so.

Slowly pour the lye solution into the oils.

Blend with a stick blender in short bursts, stirring in between, until the mixture reaches trace, when drips sit on the surface for a moment before sinking, like thin pudding.

Stir in the essential oil, if using.

Pour into molds and tap them on the counter to settle any air bubbles.

Leave the bars in the molds for 24 to 48 hours, until firm enough to unmold cleanly.

Set the bars on a rack in a dry spot with good airflow for 4 to 6 weeks, turning them now and then, before using.

Between uses, keep bars on a draining soap dish so they dry completely.