Preheat oven to 175C. Line a baking sheet with aluminum foil and lightly coat with cooking spray.
If almonds and cashews are untoasted, toast the almonds and cashews (separately) in a saucepan over medium heat until roasted ( ~ 5 minutes for almonds and ~7 minutes for cashews)
Combine walnut halves, pecan halves, almonds, and cashews in a large bowl. Add ground cumin, smoked paprika, sea salt and black pepper; toss to coat.
Heat the brown sugar, water, and butter in a small saucepan over medium heat until the butter is melted. Cook for 1 minute and remove from heat. Slowly pour butter mixture over the bowl of nuts and stir to coat.
De-stalk the kaffir lime leaves and cut into rough bits. Stir in the kaffir lime leaves to the butter syrup nuts mixture and get ready to bake.
Transfer nuts to the prepared baking sheet and spread into a single layer. Bake the nuts in the pre-heated oven for 10 minutes (1st bake).
Remove from oven and stir nuts until the warm syrup coats every nut evenly. Spread into a single layer and return to the oven for 2nd bake until nuts are sticky and roasted, about ~ 7-8 minutes.
Allow to cool before serving or bottling.