Roughly chop up soap bar and place pieces in a blender or food processor along with the oatmeal. Pulse until you get a fine powder.

Put soap and oatmeal powder in a bowl. Mix in oil, water, and any essential oils you may want.

Use your hands to mold the soap. Leave a deep well in the center and push the rope in, then form the soap around it.

Let soap dry for at least 24 hours.