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.
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.
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.
Break brittle into pieces. Store airtight up to 2 weeks.
YUM! I made this with peanuts because I didn't have cashews and didn't roast them since they were already roasted. The combination tastes really good, but there were a few too many peanuts and I think not having them warm made a difference in how fast the sugar cooled. I had a hard time getting it spread before it hardened. I would recommend pouring as soon as everything is combined, whether it's still foaming or not.
I'll definitely do this again, most likely with cashews or almonds. If I do the peanuts again, I'd chop them a tiny bit first.
I used a canned delux mixed nut with sea salt for this. It was wonderful with a mix of almonds, filberts, cashews, pecans and brazil nuts! I made this the first year it came out, and then lost the recipe. I'm oh, so glad that I found it here again!!!!