But, I wanted something easier and making the powder version is.
First, I grated one bar of Fels-Naptha soap. I used a large zester, which is a really fine grater, to do this.
I worked great. It made a very fine shred which was easy to mix with the powder ingredients.
Then I added one cup each of Borax, washing soda and baking soda.
After breaking up the larger chunks of Borax and washing soda with my hands, I mixed it together really good.
I'm storing it in a Mason jar. Just two tablespoons for a large dirty load or one tablespoon for a smaller load. This recipe should be good for about 30 loads of laundry.