Adjust oven rack to center position and preheat oven to 225°F. Combine all ingredients in a food processor and pulse until a very rough puree is formed, about 15 short pulses, scraping down sides as necessary. Transfer mixture to a parchment or Silpat-lined rimmed baking sheet and spread in a thin, even layer.
Transfer to oven and cook until fully dehydrated and crackly, 4 to 6 hours. Let mixture rest in the oven with the door left ajar until completely cool, about 1 hour.
Transfer mixture to a food processor and process until a rough powder is formed. Store mixture in a sealed container in a dark, cool place for up to 2 months.
