Step 1

Line an 8-inch square baking dish with aluminum foil.

Step 2

In a medium saucepan over low heat, combine condensed milk, chocolate chips, and butter; cook until chocolate is melted and smooth, stirring constantly. Remove from heat; stir in vanilla. Pour chocolate mixture evenly into baking dish.

Step 3

Pour caramel sauce over top of fudge and using a knife, swirl caramel into fudge. Sprinkle with salt, cover, and refrigerate at least 6 hours, or until firm.

Step 4

Remove foil and cut into 1/2-inch squares. Store in refrigerator.