Preheat oven to 350°F and line a 9x9-inch baking pan with parchment paper, leaving overhang for easy removal.
Combine melted butter and brown sugar in a large bowl, stirring until well mixed.
Add eggs one at a time, mixing fully after each, then stir in vanilla extract.
In a separate bowl, whisk together flour, baking powder, and salt.
Add half of the flour mixture to the wet ingredients and stir until incorporated.
Add the remaining flour mixture and mix until the batter is smooth.
Fold in chopped pecans and butterscotch chips, scraping the bowl to mix evenly.
Spread batter evenly in the prepared pan.
Bake for 25 to 30 minutes until the top is golden, shiny, and slightly cracked, checking doneness at 25 minutes.
Allow the brownies to cool completely before lifting out and cutting into servings.