Generously butter a cookie sheet and set aside. In a microwave safe bowl (make sure it is microwave safe! I assumed my first bowl was and it melted a hole through the bottom!) add the sugar and corn syrup and mix. Put in the microwave and cook for 3 minutes. Stir. Put back into the microwave and cook for an additional 3 minutes. The mixture should start looking like an amber color.
Stir in the cashews. Cook for an additional 3-5 minutes. I suggest checking after each minute. If the color looks golden brown then it is good to go. I cooked my first batch too long the first time and it burnt some of the nuts.
Once the mixture is a golden brown, remove from the microwave and stir in the butter and vanilla. Continue cooking for an additional minute. Remove and stir in the baking soda. It will start to foam and become thick.
Spread the mixture on the buttered baking sheet and allow to completely cool. Break into pieces. Can be stored at room temperature in an airtight container for up to 3 days.