Preheat oven to 350F. Line an 8x8-inch baking pan with parchment paper.

Melt butter over medium heat, remove from heat, and stir in chocolate. Stir until everything is melted and smooth. Set aside to cool.

In a large mixing bowl, stir together granulated sugar, brown sugar, eggs, vanilla, and peanut butter. Stir in cooled chocolate mixture. Add flour and salt and stir until just combined. Pour batter into prepared pan and sprinkle with chopped pretzels.

Bake 55 - 60 minutes or until a toothpick inserted into the center comes out mostly clean.

Cool on a wire rack before slicing.