Butter a cookie sheet. Combine sugar and corn syrup in a 2 quart glass bowl and microwave on high 4 minutes. Stir in peanuts and microwave on high 3 1/2 minutes more, then stir in butter and vanilla and microwave for 1 1/2 minutes.
Stir in baking soda until light and foamy. Pour onto cookie sheet and spread thin. Cool completely and break into pieces and serve.
