Clean well to remove any traces of dirt

Trim off any brown bits

Halve the onion or leek lengthwise, and then cut cross-wise into 1" pieces

Dehydrate at 125 deg F until brittle (~12 hrs)

Grind the large dried pieces in a food processor to coarse flakes - if it is starting to clump, then there is too much moisture

Return them to the dehydrator, if they are clumping, at 125 deg F for 8-12 hours longer

Process further into powder

Store in an airtight container in a cool, dark spot