Preheat oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper or lightly grease it.

1. In a large bowl, stir together melted butter, brown sugar, and granulated sugar until smooth.
2. Let the mixture cool slightly, then whisk in the eggs and vanilla extract.
3. In a separate bowl, whisk together flour, baking powder, and salt.
4. Gradually mix the dry ingredients into the wet ingredients until fully combined.
5. Fold in 1 cup of the crushed pretzels.
6. Spread half of the batter evenly into the prepared baking pan.
7. Drizzle half of the caramel sauce over the batter and gently swirl with a knife or spatula.
8. Spread the remaining batter over the top and drizzle with remaining caramel, swirling again.
9. Top with remaining pretzels and a sprinkle of flaky sea salt if using.
10. Bake for 25–30 minutes, or until the top is golden and a toothpick inserted in the center comes out with moist crumbs.
11. Cool completely in the pan before slicing into bars.