1. Line a 10- by 15-inch baking pan with cooking parchment; generously butter parchment (or generously butter a nonstick pan). Spread cashews in another baking pan. In a 350° regular or convection oven, bake until golden brown, 8 to 10 minutes.
2. Combine sugar, corn syrup, and 1 cup water in a 2- to 3-quart pan. Set over medium heat and stir just until sugar is dissolved, 4 to 5 minutes. Increase heat to high and boil without stirring until syrup is amber-colored (330° to 335° on a candy thermometer; see notes), 12 to 20 minutes. When sugar begins to brown around edges of pan, swirl mixture in pan gently to ensure that syrup caramelizes evenly.
3. Remove from heat and, working quickly, carefully stir in warm cashews and the five spice and salt. Mixture will foam; when foaming subsides slightly, pour mixture into prepared baking pan and use a heatproof flexible spatula to spread into a thin, even layer. Let stand in a cool, dry place until cool and hard to touch, at least 1 hour.
4. Break brittle into pieces. Store airtight up to 2 weeks.
Nutritional analysis per ounce.