Line your counter with wax paper.
In the bowl of a stand mixer, add peanut butter, softened butter, brown sugar and powdered sugar. Turn mixer on low until powdered sugar is mixed in. Turn up to medium and continue beating until smooth.
Stir in 1 cup of mini chocolate chips. (optional). Mix well.
Using a small scoop, scoop about 1/2 tablespoon of peanut butter mixture and roll into a ball. Press between two pretzels and set on wax paper. Continue until all of the peanut butter mixture is gone.
In a small bowl, add semi-sweet chocolate chips and shortening. Microwave for one minute and then stir well. Continue microwaving for 20 seconds at a time, stirring well after each time, until it is completely smooth.
Dip each pretzel sandwich in the chocolate, tapping it on the edge to remove excess chocolate. Then set back on wax paper and allow the chocolate to harden.