Combine the chocolate chips, 3/4 of the sweetened condensed milk, 1 tsp of the vanilla, salt and butter in a saucepan. Turn the heat to medium-low. Using a wooden spoon, stir frequently until the chocolate is melted. It should be nice and creamy. Add the vanilla and stir. Turn the heat off.
Pour the chocolate mixture into a wax paper lined 8x8 pan, spreading evenly. Allow to sit.
Next, combine the peanut butter, rest of the sweetened condensed milk and salt into a different saucepan.Heat on medium-low, stirring frequently, until nice and creamy. Add the remaining vanilla and stir.
Spread the peanut butter mixture on top of the chocolate.
Using a thin skewer or butter knife, start making swirls in the fudge. You are essentially combing the chocolate and peanut butter in a swirl pattern.
Cover and refrigerate for a few hours until the fudge is hardened.
