CAUTION: Make sure you are super careful not to touch the liquid during the cooking process, and do NOT lick the spoon. It's wicked hot and can burn. I know it's tempting but don't do it!!
Place a rimmed cookie sheet aside for the finished candy.
In a large glass measuring cup, or microwave safe container, combine sugar and corn syrup. Stir with a spoon.
Place the measuring cup in the microwave and cook for 4 minutes. The mixture is going to get extremely hot so don't touch the mixture by accident, or on purpose. Use your noggins, peeps.
Remove the measuring cup from the microwave and add the peanuts to the measuring cup and microwave on high heat for 3 minutes. Again, don't touch the mixture, it's flipping hot!
Next, remove the measuring cup from the microwave and add butter and vanilla, it may bubble up, it's okay, just stir until well combined. Place back in the microwave and cook on high for 1 minute. Again, do not touch it, this stuff is piping hot.
Now add the baking soda to the measuring cup and mix for about 20 to 30 seconds while the foaming slows down. Once it's all settled you can pour it onto an ungreased cookie sheet, or large pan. Smooth out with a scraper or the back of a spoon. I spray the back of a spoon with non-stick spray then smooth mine. If desired you can toss some demerara sugar over top of the surface. Allow the candy to cool completely.
Cut with a knife or a toffee hammer to break the peanut brittle into pieces. You can eat it right away or store it in airtight container.