In a mixing bowl, beat together peanut butter, butter, powdered sugar, and brown sugar until smooth.
Scoop about 1 teaspoon of the mixture and form into a ball. Sandwich it between two pretzels.
Place on a baking sheet lined with parchment paper and freeze for 20–30 minutes until firm.
Melt chocolate chips with coconut oil (if using) in the microwave in 30-second intervals, stirring until smooth.
Dip each pretzel sandwich halfway into the melted chocolate and return to parchment paper.
Refrigerate until chocolate is set, then serve or store in an airtight container.