I love cashews so this is his answer for a brittle." Mix baking soda, 1-teaspoon water and vanilla and set aside. Mix sugar, 1/2-cup water and the corn syrup in a copper constant stir kettle. Cook over medium heat until 240 degrees on a candy thermometer. Add butter and cashews. Cook until 300 degrees on candy thermometer.
I strongly encourage using a flaky sea salt like Maldon for topping this. Line a large rimmed baking sheet with a silpat mat or parchment paper (or spray with nonstick spray). Add the sugar, water, corn syrup, and butter to a large saucepan. Measure out the baking soda and cashews and have them ready.
Stir in butter and cashews. Cook about 13 minutes, stirring constantly, to 300°F or until small amount of mixture dropped into cup of very cold water separates into hard, brittle threads. (Watch carefully so mixture does not burn.) Immediately remove from heat. Quickly stir in baking soda mixture until light and foamy.
For traditional peanut brittle, substitute 3 cups unsalted raw Spanish peanuts for the cashews. I made this as written and found it wonderful! My friends said it was the best brittle they have every had! I used both my thermometer and ice water to double check and found the 14 minutes to be spot on!