Line an 8x8 pan with parchment paper, bottom and sides. A little fancy folding will get you there with one piece.
Melt half of the milk chocolate and shortening in a microwave safe dish on 50% power for 2 minutes and stir. Microwave again on 50% power for 1 minute and stir. If needed, microwave on 50% power for 30 seconds. Stir until smooth.
Pour melted chocolate into pan. Spread on bottom and up the sides of the pan with the back of a spoon.
Freeze, for a couple of minutes while making filling, to start to harden chocolate.
There are two versions of this filling. 1) Use half of the filling ingredients, except use two extra tbsps butter, for a nicely sized filling. 2) Use all of the filling ingredients for those whom like peanut butter.
Melt and mix butter, salt, and peanut butter in a small sauce pan over medium heat. Mix in powdered sugar until smooth. Mix in graham cracker crumbs until smooth. Smooth warm filling onto set up chocolate and freeze again for a half hour to harden peanut butter mixture.
Melt the other half of the chocolate mixture as in the previous directions. Pour and spread melted chocolate onto top of firmed up peanut butter filling. Refrigerate until set.
Bring up to room temperature.
Using parchment paper, remove from dish and divide into squares. I use a pizza wheel or a chef's knife for a cutter.
Refrain from inhaling the entire contents of this recipe.
This is the closest I've been able to come to that famous store brand of peanut butter cups. Varying brands of chocolate chips will modify the flavor of this delight.
Technique: Add layer to layer while the previous layer is still not quite firmly set so that the boundaries between the layers will melt just a little and cohesion is better. That way the squares, when cut, will stay stacked together instead of separating.