Spray 8x8 pan with Pam or equivalent non-stick spray.
Measure out rice krispies and chop Butterfinger pieces before you actually make the rice krispies.
Use a large-sized pan and on low-medium heat, melt butter and peanut butter together, stirring frequently.
After melted, add in marshmallows and melt, stirring frequently.
Remove from burner, and add in the rice krispies until well mixed.
Measure out approximately 1/4 cup out of the chopped Butterfinger pieces for the topping and set aside.
Add the rest of the chopped Butterfingers to the rice krispies and mix well.
Immediately pour the mixture into the 8x8 pan and spread, then press evenly. (I placed waxed paper on top and pressed the mixture down without getting my hands all sticky).
After the rice krispies have cooled, cut them evenly into 9 even pieces and place about 1/2 inch apart on waxed paper.
Melt the milk chocolate chips and shortening either on the stove or microwave. (I use the microwave, with 30 second intervals - normally a total of 1 -1/2 minutes).
Take a ziploc bac and pour chocolate into bag. Cut a very small snip on corner of ziploc bag and squeeze the chocolate to the corner to start drizzling chocolate on each of the treats.
Then take the 1/4 cup of chopped Butterfingers that were set aside, and sprinkle on all the treats.
With remaining chocolate, drizzle chocolate on top of butterfinger layer.
Place the krispie treats in the refrigerator for 10 minutes to set the chocolate, (don't leave in longer) then remove them from the refrigerator and store them in a covered container.