Whisk the egg whites until light and fluffy, but not stiff.
Mix in all of the other ingredients until coated well.
Pour into the slow cooker and cook on HIGH. Leave the lid on, but slightly ajar to let the moisture out. Stir it gently just to check it's not sticking after 1 hour. It will take 2-3 hours to cook. Stop it cooking when it's just starting to get crunchy (it won't be fully crunchy, only around the edges, the rest will 'crunch' as it cools.)
Pour it out onto a baking sheet or sheet of baking paper to let it cool and harden. Store in an airtight container when it's cold.
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