In a heavy saucepan over low heat, melt white chocolate squares, sweetened condensed milk, and salt. Remove from heat; stir in crushed cookies.

Spread evenly into a wax paper-lined 8-inch square pan. Chill in the refrigerator until firm, about 2 hours.

Turn chilled fudge onto a cutting board; peel off wax paper. Cut fudge into squares. Store leftovers covered in the refrigerator.