Line a quarter cookie sheet with parchment paper.
Add the sugar, corn syrup, and water to a medium sauce pan and heat over medium heat. Cook mixture until the sugar is dissolved, and comes to a low boil, stirring occasionally. 2 cups granulated sugar, 1 cup light corn syrup, 1/2 cup water
Attach the candy thermometer to the pan, making sure it is submerged in the candy mixture. Continue cooking until the temperature hits 250 F.
Add the peanuts, and stir them into the mixture. 2 cups chopped salted and roasted cashews
Stir constantly until the mixture reaches 300 F.
Remove the pan from the heat and stir in the butter, vanilla, and baking soda. 2 TBS butter, 2 tsp vanilla extract, 1 1/2 tsp baking soda
Carefully pour the mixture onto the prepared pan, pouring it out of the pan, and spreading around the top as you pour. Or spooning it out of the pan.
Spread the thick parts lightly with a spatula to thin them out, and tip the pan around to spread it out as well. The less you spread it, the more light the texture will be.
Let the candy cool completely for 30 minutes, to 1 hour, before breaking into pieces and eating.
Store the peanut brittle in an airtight container at room temperature for up to 2 months, as needed.