LINE 8- or 9-inch square pan with wax paper, extending paper over edges of pan.
MELT peanut butter chips and peanut butter with sweetened condensed milk in heavy saucepan over low heat. Remove from heat. Stir in peanuts and vanilla. Spread evenly in prepared pan.
CHILL 2 hours or until firm. Remove from pan by lifting edges of wax paper; peel off paper. Cut into squares.
TIP: MICROWAVE METHOD: Combine peanut butter chips, sweetened condensed milk and peanut butter in microwave-safe bowl. Microwave on HIGH (100% power) 3 minutes or until chips melt, stirring after 1 1/2 minutes. Proceed as above.