Line an 8- inch square pan with foil and grease foil. Mix sugar and cocoa in heavy 3 quart saucepan. Stir in milk and butter. Bring to a boil over medium heat, stirring constantly. Without stirring, boil vigorously 5 minutes. Remove from heat; add chips and stir until melted and smooth. Spread 1 cup in lined pan, top with cookies, then spread remaining fudge evenly over the top. Refrigerate 6 hours until firm. Invert pan, peel off foil, invert fudge and cut in 1-inch squares.