Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, combine the melted butter and brown sugar. Whisk them together until smooth and well combined.
Add the eggs one at a time, mixing well after each addition. Then stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt. Gradually fold the dry ingredients into the wet mixture until just combined. Be careful not to overmix.
Gently fold in the butterscotch chips and chopped pecans, if using, until evenly distributed.
Pour the batter into the prepared baking pan, spreading it evenly across the surface.
Bake for 25-30 minutes, or until the edges are golden and a toothpick inserted in the center comes out with a few moist crumbs.
Remove from the oven and allow the blondies to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.