Place butterscotch chips and peanut butter in a microwave-safe bowl. Heat in the microwave for 1 minute; stir until smooth. Refrigerate for about 10-15 minutes, stirring every few minutes, until mixture is thick enough to scoop.
Scoop mixture into roughly Tablespoon-sized balls and place onto prepared pan. Refrigerate until ready to use.
Make the cookies:
Preheat the oven to 350F degrees and line a baking sheet with parchment paper.
In a large bowl using a hand-held mixer or a stand mixer fitted with the paddle attachment, cream the butter, peanut butter, and brown sugar together on high speed until lightened and fluffy. Beat in the egg and vanilla until combined.
Add the flour, baking soda, and salt, and continue to beat on low until mixture forms a dough.
Place granulated sugar in a small bowl. Use your hands to scoop out about 2 Tablespoons of dough, flatten, place a peanut butter truffle in the center, wrap the dough around the truffle, then roll into a ball, making sure that the dough is fully sealed around the truffle.
Place on the prepared baking sheet, and flatten cookie slightly. Roll in sugar. Repeat with the remaining truffles and dough.
Bake cookies for 9-10 minutes, or until cookies look puffed and edges are set. Allow to cool on the baking sheet for 10 minutes before transferring to a wire rack to cool completely.
*As the cookies cool, the filling will thicken up. If you want super ooey gooey drippiness, heat in the microwave for 5-10 seconds!