1. Line 8-inch square pan with foil.
2. Place peanut butter chips and 1/2 cup sweetened condensed milk in small microwave-safe bowl. Microwave at MEDIUM (50%) 1 to 1-1/2 minutes, stirring after 1 minute, until chips are melted and mixture is smooth when stirred. Stir in 1/2 teaspoon vanilla; spread evenly in prepared pan.
3. Place remaining sweetened condensed milk and chocolate chips in another small microwave-safe bowl; repeat above microwave procedure. Stir in remaining 1/2 teaspoon vanilla; spread evenly over peanut butter layer.
4. Cover; refrigerate until firm. Remove from pan; place on cutting board. Peel off foil. Cut into squares. Store tightly covered in refrigerator. About 64 pieces or 1-1/2 pounds.
NOTE: For best results, do not double this recipe.