Preheat oven to 150C/300F. Line a large baking sheet with parchment paper and set aside.
In a small bowl, whisk together the sugar, cinnamon, and salt.
In a large bowl, whisk the egg whites with water until foamy.
Add the cashews to the egg white mixture, ensuring they are all well coated. Add the sugar mixture and mix until combined.
Transfer the cashews onto the baking sheet, ensuring they are spread out in a single layer. Bake for 20-25 minutes, stirring several times throughout.
Let the candied cashews cool for several minutes before giving them another mix and letting them cool completely.
Notes
Stovetop method: Heat a large skillet over medium heat. When the pan is hot, add the sugar, cinnamon, salt, and water and combine. Stir consistently to prevent burning. Once the sugar has dissolved, add the cashews and coat them in the syrup. Continue stirring the mixture until the liquid crystallizes on the cashews. Remove from the pan, spread them out, and let them cool completely.
Leftovers: Keep at room temperature for up to one month or in the freezer for up to 6 months.