Combine corn syrup and butter in 2-quart saucepan. Cook over low heat, stirring occasionally, until butter melts. Remove from heat; stir in peanut butter. Cook and stir over low heat until smooth. Remove from heat.

Add powdered sugar and vanilla. Beat until smooth with wooden spoon.

Spread in greased 8-inch square baking pan. Refrigerate 2 hours or until firm. Cut into 1-inch squares.