First you take an Ivory soap bar. Then you put it on a paper towel and zap it in the microwave for three minutes.
You end up with the most amazing soap cloud that crumbles beautifully into powder. Did three bars for my giant bucket of homemade laundry soap.
The mini men loved watching the cloud grow and shouted gleefully when it neared the top of the inside of the microwave. A truly successful Pin that doubled as a science experiment as well as saved momma a whooooole lotta time and arm strength not grating those three bars!