Step 1. Prep a 8 X 8 inch baking pan with non-stick spray. Step 2. Line the baking pan with parchment paper that will overhang on all four sides of the pan.
Peanut butter Layer: Step 1. Add butter, peanut butter, and vanilla in a medium size bowl. Put in the microwave for 90 seconds. Stir well. Step 2. Add powder sugar, stirring to mix all of the ingredients together. Continue to stir until the mixture is smooth. Step 3. Pour this into the prepared baking pan. Spread with an offset spatula to make sure that the top is even. Set aside.
Chocolate Layer: Step 1. Add the milk, chocolate chips,butter, and vanilla to a medium microwave safe bowl. Step 2. Microwave for 90 seconds. Step 3. Stir. Keep stirring until the mixture is creamy. Pour this over the peanut butter layer. Step 4. Use a spatula to spread the chocolate layer over the peanut butter layer. Set aside.
Topping: Step 1. Spoon the melted chocolate into a piping bag. Set aside.
Step 2. Spoon the melted peanut butter into a piping bag. Set aside. Pipe lines across the chocolate layer. Step 3. Use a butter knife to pull this through to create a zigzag design. Put this in the refrigerator to chill for 4 hours. Step 4. Lift the fudge out of the baking dish by lifting the parchment paper on all 4 sides. Place on the counter and cut into bite-size pieces.