Grind soap flakes on “low” in high-powered blender or food processor until it resembles coarse sand, making sure it does not blend so much that it melts.
If you cannot find soap flakes, grate a plain, unscented soap bar.
Grind rosemary in mortar & pestle or spice grinder.
Mix all ingredients in a bowl until well incorporated and store in airtight container or mason jar for up to 2 years.
Notes
To use: Sprinkle powder as needed across sinks, tubs, and tile floors. Scrub with a wet brush or sponge. Rinse thoroughly with warm water.