Gather all ingredients. Line a mini muffin pan with paper (or foil) liners and a baking sheet with parchment paper (or a silicon baking sheet) and set both aside.
In a medium pot combine the butter, brown sugar and peanut butter over medium heat.
Slowly and continuously stir the mixture until it is smooth and bubbling slightly.
Note: if you leave the peanut butter on heat for too long without stirring it will burn, you would still be able to use the peanut butter, but it would taste slightly burnt.
Remove from heat and add the powered sugar 1/4 cup at a time.
Note: once most of the powdered sugar has been mixed into the peanut butter it will become really tough to mix. This is the correct consistency that you want.
Once all the powdered sugar is completely mixed in, set aside to cool.
While you are waiting for the peanut butter to cool, combine the chocolate chips and vegetable shortening in a microwaveable container.
In 20 second bursts, microwave the chocolate chips until the mixture is smooth. Mix well between each 20 seconds.
The type of chocolate you use is not that important, my first batch I used half milk chocolate and half semi-sweet and it was great. Choose the chocolate to suit your tastes.
Once the chocolate is completely melted pour (or scoop) it into the paper liners. Covering approximately 1/4 of the cup.
Slightly shake the tray to even out the chocolate. Place in the fridge for 30 minutes to harden.
Once the bottom layer of chocolate is in the fridge, scoop the peanut butter filling into balls, just smaller than the diameter of the muffin cup. Flatten the top and bottom so they look like disks.
Note: at this point you can put the peanut butter in the fridge but I found they were cooled down enough by just staying on the counter.
Once the chocolate is cooled place a peanut butter disk on top of each, placing it as close the the middle as you can, leaving as much room for the chocolate to go on top as possible.
Note: in my first batch I didn't flatten out the balls, and it made pouring the top layer of chocolate quite difficult.
Pour the remaining chocolate over the cups evenly. The chocolate mixture may need to be reheated slightly. Put the finished cups back in the fridge for 30 minutes to cool.
This recipe makes approximately 48 mini cups, however if the peanut butter balls were made a slight bit smaller you would get more.
There is the final product, which tastes pretty close to a Reese's peanut butter cup. Enjoy!