Line an 8×8-inch baking dish with parchment paper, leaving some overhang on the sides so it’s easy to lift out later. Lightly spray with nonstick cooking spray.
In a medium saucepan over low heat, combine the chocolate chips, sweetened condensed milk, and butter. Stir constantly until everything is melted and smooth. Keep the heat low so the chocolate doesn’t scorch.
Remove the pan from the heat and stir in the vanilla extract and salt.
Fold in 1½ cups of the chopped candy bars, saving the rest for the top.
Pour the fudge into the prepared pan and spread it into an even layer.
Drizzle melted chocolate over the top, then sprinkle on the remaining ½ cup of candy bars. Gently press them into the surface so they stick.
Refrigerate for 3 to 4 hours, or until the fudge is completely set.
Lift it out using the parchment paper, place on a cutting board, and cut into squares.