Line large baking sheet with parchment paper* and set aside. 
Mix sugar and corn syrup in very large microwavable glass bowl until moistened. 
Microwave on high 5 minutes. 
Stir in butter and peanuts. 
Microwave 3 minutes or until golden brown (caramel colored). 
Add baking soda and vanilla.  Will foam. 
Mix well. 
Immediately pour as thinly as possible onto prepared baking sheet. 
Cool completely, and break into pieces.

*Rather than lining with parchment paper, you can just butter pan if you choose.