Line a mini-muffin tin with paper liners; set aside. Line a baking with parchment paper; set aside.
In a medium saucepan, combine the peanut butter, butter and brown sugar over medium heat. Heat until completely melted and starting to bubble a little, stirring constantly. Remove from the heat. Add the powdered sugar a ¼ cup at a time, stirring until completely combined with the peanut butter mixture after each addition. Set aside and let cool.
Meanwhile, melt the chocolate chips and shortening together in the microwave on 50% power in 30-second increments, until completely melted, stirring after each burst.
Using a small cookie scoop or a couple of teaspoons, spoon melted chocolate into the bottom of each lined muffin cup.
Use a heaping teaspoon to scoop out the peanut butter mixture. Roll it into a ball, and then flatten it slightly into a disk. Place on the prepared baking sheet lined with parchment paper. Once finished with all of the peanut butter mixture, refrigerate both the muffin tins and the peanut butter patties for about 30 minutes.
Place a peanut butter patty on top of each chocolate-lined muffin tin. Then use a scoop or spoon to add more melted chocolate on top and around each peanut butter patty. (If the melted chocolate firmed up, just pop it back into the microwave at 50% power for 30 seconds or so to re-melt.)
Refrigerate again for 30 minutes, then they're ready to serve! Store in the refrigerator for up to 1 month or in the freezer for up to 3 months. You can keep at room temperature in an airtight container if you're going to serve them the same day, but they'll start to get soft if not at cool room temperature.
You can substitute milk chocolate chips for the chopped milk chocolate.
You can substitute refined coconut oil for the vegetable shortening.
You use different nut butters, I recommend using "processed" versions; the "natural" version of nut butters will be too oily for the filling.