In your microwave-safe bowl, combine the 1 cup granulated sugar and 1/2 cup light corn syrup. Stir them together until well mixed.
Microwave the mixture on high for 4 to 5 minutes. Keep an eye on it as it cooks; the mixture should bubble and become a light golden color.
Carefully remove the bowl from the microwave (it will be hot!). Stir in the 1 cup chopped cashews and 1 tablespoon salted butter until everything is well combined.
Mix in the 1 teaspoon vanilla extract and 1 teaspoon baking soda. The baking soda will cause the mixture to foam up, creating a light and airy texture in your brittle.
Quickly pour the mixture onto a parchment-lined baking sheet. Use a spoon or spatula to spread it out evenly to your desired thickness.
Allow the brittle to cool completely. This usually takes about 30 minutes to an hour. Once it’s set, break it into pieces.
