Combine first 3 ingredients in a saucepan, reserving condensed milk can. Cook over medium-low heat until all morsels melt, stirring often. Remove from heat; stir in vanilla and salt. Cool slightly (about 15 minutes).
Meanwhile, grease an 8" round cake pan or springform pan with butter. Line pan with 2 pieces of plastic wrap, overlapping edges and smoothing out any wrinkles. Wrap empty condensed milk can with aluminum foil, smoothing out wrinkles; place in center of cake pan.
Stir 1 cup candies and crushed cookies into fudge; spread fudge in cake pan, holding can firmly in center. (A second pair of hands is a big help here.) Sprinkle remaining 1/4 cup chocolate candies over fudge, gently pressing candies into fudge. Cover and chill until firm (about 2 to 3 hours).
To unmold, carefully loosen edges with a sharp knife, and remove can from center of fudge. Carefully invert fudge onto a plate. Invert again on a serving plate or cardboard cake round for gift giving. Cut fudge into thin slices to serve.
Note: For an easy gift giving "platter," we wrapped a cardboard cake round with wrapping paper.