Grate the castile soap with a grater.
Put the grated castile soap pieces in a food processor bowl. Pulse until only large crumbs (no chunks) remain.
Add baking soda to the food processor and pulse until ingredients are in powder form and combined (about 1 minute).
Add washing soda to the food processor and repeat pulsing until combined well.
Dump the mixture into a storage container and add borax and OxiClean. Combine well with a spoon.
Add the essential oils, if using, (optional) and mix well.
Store detergent in an air-tight container to help avoid clumping.
Simply add about 2 tablespoons directly into your washer bin with your clothes (you might want to only use 1 tablespoon for HE front loaders. Add more, if desired, for larger or more heavily stained loads.