Line a greased 9" square pan with aluminum foil; set aside.
Combine first 3 ingredients in a medium saucepan. Cook over medium-high heat, stirring constantly, until mixture comes to a boil; cook 3 minutes, stirring constantly. Remove from heat; add white chocolate morsels, marshmallow cream, 2 cups crushed cookies, and salt. Stir until morsels melt.
Pour fudge into prepared pan. Sprinkle remaining 1 cup cookies over fudge, gently pressing cookies into fudge. Cover and chill until firm (about 1 to 2 hours).
Lift uncut fudge in aluminum foil from pan; remove foil, and cut fudge into squares.