Slice or dice onions
Add to slow cooker
Cook on low for 4-6+ hours
Drain onions (use that for a meal later)
Spread onions on dehydrator trays
Dry at 125°F / 52°C for 8-12 hours
Condition
Store in an airtight container
Add dehydrated onions to your favorite grinder
Pulse a few times, then blend into a find powder
Redry the powder
Store in an airtight container with arrowroot powder to help stop clumping