Microwave first 3 ingredients in a 2-quart glass bowl on HIGH 5 minutes, using an 1100-watt microwave oven. (Microwave 1 more minute if using a 700-watt microwave.) Stir in peanuts. Microwave 3 more minutes in an 1100-watt oven (add 1 more minute in 700-watt oven). Stir in butter and vanilla. Microwave 45 seconds in an 1100-watt oven (add 1 more minute in 700-watt oven) or until candy is the color of peanut butter. Stir in baking soda (mixture will bubble). Working quickly, spread hot candy in a thin layer onto a lightly greased baking sheet using two metal forks. Cool completely. Break candy into pieces.