1Heat the oven to 400°F and arrange a rack in the middle. While the oven is heating, place cashews on a baking sheet and toast in the oven, stirring occasionally, until deep brown, about 12 to 15 minutes. Cool slightly on a cutting board, then coarsely chop; set aside.
2When the oven is ready, place bacon on a baking sheet and roast until deep brown and well done, about 15 minutes. Remove to a paper-towel-lined plate to cool; reserve 1 tablespoon of the rendered bacon fat. Line a baking sheet with parchment paper, coat the paper with a thin layer of the reserved fat, and place the baking sheet on a cooling rack. Crumble bacon into bite-sized pieces; set aside.
3Combine sugar and water in a medium saucepan over high heat and stir until sugar has dissolved, about 3 minutes. Cook, swirling the pan occasionally (do not stir), until mixture is deep amber and registers 350°F on a candy thermometer, about 10 to 15 minutes. Immediately remove the pan from heat.
4Carefully add cashews, bacon, and salt to the caramel and stir to combine. Immediately pour mixture onto the center of the prepared baking sheet. Let sit at room temperature until hardened, about 20 minutes. Let cool completely, then break into shards.