LINE 8- or 9-inch square pan with wax paper, extending paper over edges of pan.
HEAT sweetened condensed milk and peanut butter in heavy saucepan over medium heat until just bubbly, stirring constantly. Remove from heat. Stir in white chocolate until smooth. Immediately stir in peanuts and vanilla.
SPREAD evenly in prepared pan. Cool.
CHILL, covered, 2 hours or until firm. Remove from pan by lifting edges of wax paper. Cut into squares.