In a large mixing bowl, combine the melted butter, crushed pretzels, crushed Ritz crackers, powdered sugar, and both types of peanut butter. Mix until all ingredients are evenly combined and form a thick, crumbly mixture.
Transfer the mixture into a greased 9x13-inch baking dish. Using a spatula, press the mixture down firmly and evenly across the bottom of the pan.
In a microwave-safe bowl, melt the milk chocolate chips in 30-second intervals, stirring in between, until smooth and fully melted.
Once melted, pour the chocolate over the pressed peanut butter and pretzel mixture in the baking dish. Use a spatula to spread it evenly across the top.
Place the baking dish in the refrigerator for at least 2 hours to allow the chocolate to set completely.
After chilling, remove the bars from the refrigerator and cut them into squares or rectangles. Serve them at room temperature.
