In a stand mixer with the paddle attachment, beat the butter & peanut butter with both sugars, until light & fluffy. Beat in the eggs & vanilla.
Add the flour, baking soda & salt, & stir until almost combined; fold in the chocolate chips & 1 cup of pretzel pieces.
Spread the the dough evenly in the pan & bake for 20-25 minutes, until golden on top.
In a small bowl, melt the peanut butter & chocolate chips in the microwave for 20-30 seconds. Stir until smooth.
Place whole pretzels in rows 4x6. Drizzle chocolate, & then sprinkle the top with the remaining ½ cup pretzel pieces. Refrigerate to help the chocolate set up. Cut 24 squares & serve.