Preheat oven to 350°F. Line a 9-by-13-inch baking pan with parchment.
In a bowl, mix flour, baking powder and salt. Using an electric mixer, beat butter and sugar until light. Beat in eggs, one at a time, then vanilla. Reduce speed to low; beat in flour mixture. Stir in chocolate chips and 1 cup pretzels. Spread evenly in baking pan. Bake until a toothpick inserted into center comes out clean, 25 to 30 minutes.
In a bowl set over a pan of simmering water, melt chocolate with peanut butter, stirring until smooth. Spread mixture evenly over blondies. Sprinkle with remaining crushed pretzels. Let cool before cutting into squares.
These tasted good, but I had some problems with my batter. It was so thick, I couldn't "spread" it in the pan. I had to push it into place, so my blondies weren't flat and pretty like theirs. They tasted good, but I don't think mine were pretty enough to serve to others. Any tips?