Heat sweetened condensed milk, the chocolate chips in microwave or on stove till it is melted. I use 30 second intervals in the microwave, stir, then repeat. You might have to do this 2-3 times. Then, add pinch of salt and vanilla extract.
Once melted, quickly, spread evenly into wax paper lined 8-or 9-inch square pan. Make sure the sides of the wax paper comes above the pan so it is easy to pull out of the pan once cool. It will thicken up quick so make sure you spread that quickly. Cover and chill 2 hours or until firm. Turn fudge onto cutting board; peel off paper. Sprinkle with chopped peanuts or sprinkles if desired. I left plain. Cut into squares. Store leftovers covered in refrigerator.
