In a medium-sized bowl, add the egg whites and vanilla; whisk until frothy, about 1 to 2 minutes.
Then whisk in the brown sugar, ground cinnamon, salt, cayenne, allspice, and maple syrup. Add the nuts and stir to coat.
Spray the inside of a 4 to 6-quart slow cooker with nonstick cooking spray and toss in the butter. It will melt as the nuts begin to candy.
Place a paper towel over the crockpot, cover and cook on LOW for 3 hours, stirring every 30 minutes as the nuts caramelize or on HIGH for 1 hour.
Transfer the nuts to a parchment-lined baking sheet. Allow them to cool and dry completely before packaging or storing.
Notes
Storing: These candied nuts will keep in an airtight container at room temperature for up to 3 weeks or in the freezer for up to 2 months.
Crisping: After removing from the slow cooker and cooling, If needed, toast the nuts on a parchment-lined baking sheet in a 450 F oven for about 5 minutes. Then, let them cool completely before breaking into clusters or individual nuts.