Combine peanut butter and butter in a medium-sized bowl and use an electric mixer to beat together until well-combined.
Stir in brown sugar, salt, and vanilla extract.
Gradually add the powdered sugar, about ¼ cup at a time, stirring until completely combined. Set aside.
Roll about 2-3 teaspoons of your peanut butter mixture into a ball, slightly flatten, and set aside on a wax paper lined cookie sheet (if the peanut butter mixture is too sticky to handle, add more powdered sugar, stirring in 1 Tablespoon at a time until it is manageable).
Set out 20 cupcake liners on a large cookie sheet.
Prepare your chocolate by combining the chocolate chips and shortening in a large, microwave-safe bowl and microwaving in 25-second increments (stirring well between each) until chocolate is completely melted.
Spoon a small amount (about 2 teaspoons) of chocolate into a cupcake liner and use the back of a small spoon or use a pastry brush to spread the chocolate so the entire bottom of the liner is covered.
Press a prepared peanut butter ball gently into the chocolate layer, and then spoon additional chocolate on top until all of the peanut butter is completely covered in chocolate.
Repeat until all cupcake liners have been filled.
Allow cupcake liners to sit undisturbed until the chocolate has hardened (this may take over an hour), or you may speed up the process and place the cups in the fridge for at least 30 minutes.