Preheat oven to 350°F. Lightly grease a 9-inch cast iron skillet (or a 9-inch baking pan) with cooking spray. Set aside.
In a large bowl, beat melted butter, brown sugar, and eggs with a hand mixer or stand mixer with fitted paddle attachment at medium speed until combined, about 3-4 minutes, stopping to scrape sides of bowl.
In a medium bowl, whisk together flour, baking powder, and salt. With mixer on low speed, gradually add flour mixture to butter mixture, beating until combined.
Press half of batter into prepared skillet. Pour ¾ cup of salted caramel over batter and then swirl with a wooden pick or butter knife.
Gently spread remaining batter into skillet. Top with remaining pretzels.