Spray an 8x8 baking dish with cooking spray. Place a piece of parchment paper on top, long enough to allow the sides some overhang. (Cut an inch or so slice into each corner of the parchment paper to make it fit better in the dish.)

In a microwave safe bowl combine the chocolate chips with 1 cup of sweetened condensed milk (spray your measuring cup with non-stick to allow it to slide back out easily), 2 tablespoons of butter, ⅛ (a pinch) teaspoon of salt and the vanilla extract.

Microwave in 30 second intervals, stirring well after each for 1 minute to 1 ½ minutes, or until the mixture is completely smooth.

Pour into the prepared dish.

In a smaller bowl, combine the peanut butter chips with the remaining sweetened condensed milk, butter and salt. Microwave in 30 second intervals, stirring after each until the mixture is smooth.

Pour the melted peanut butter over the chocolate mixture and use a knife to swirl the peanut butter into the chocolate.

Refrigerate for at least 3 hours but up to overnight.

Using the overhang parchment paper, lift the fudge out of the dish. Slice into 16-20 squares.