1Line bottom and sides of 8-inch square pan with foil, leaving foil overhanging 2 opposite sides of pan. Spray foil with cooking spray.
2In 4-quart saucepan, melt chocolate chips, condensed milk and salt over low heat, stirring constantly, until mixture can be stirred smooth. Stir in vanilla. Stir in pretzels. Spread in pan (mixture will be thick).
3In small microwavable bowl, place white chocolate. Microwave uncovered on High 30 seconds or until softened; stir until chocolate can be stirred smooth. Drizzle over fudge. Refrigerate 1 hour or until set. Use foil to lift fudge out of pan. Cut into 8 rows by 8 rows.