Dry at 125F / 52C for 10-18 hrs until they are crisp when cooled.
Store in an airtight container
Place pieces into your favorite blender or coffee grinder
Process until finley ground
Place onto cookie sheets in warmed (but off) oven to dry
Store in airtight container
Notes:Many people find onions overpowering to dry inside, so opt to do in another room with windows open, or do it outside.You can blanch the onions for a few moments beforehand to reduce the smell, or caramelize them completely for a different flavor.