Spray a 14x5 tart pan with non-stick spray.
Add the sweetened condensed milk to a saucepan. Put the chocolate morsels and butter on top of the sweetened condensed milk. Place the saucepan over medium low heat. Using a wooden spoon, stir until the fudge is melted and smooth. Spread the fudge evenly into the prepared tart pan. Sprinkle the fudge with crushed candy canes, if using.
Refrigerate until set, then remove the fudge from the tart pan by pressing up from the bottom. Slice the fudge in bite-sized squares. I like to store my fudge in a covered tin in the refrigerator.