Add sugar and corn syrup to a medium glass microwave-safe bowl. Stir together.
Microwave for 3 1/2 minutes at 100% power.
Stir in peanuts and microwave for 3 minutes.
Stir in butter and vanilla and microwave 1 minute.
Stir in baking soda and quickly pour out onto prepared cookie sheet.
Tilt cookie sheet to get mixture to spread out. Note: It helps if the cookie sheet is warm. You can place it in a warm oven while you are microwaving the brittle.