Preheat your oven to 350 degrees Fahrenheit. By starting with a preheated oven, you'll ensure that your Brown Butter Blondies bake evenly and come out with a beautiful golden color.
Grease a 9-by-13-inch baking pan with cooking spray. Then, line the pan with pre-cut parchment paper. This will make it easier to remove the blondies once they are cooled.
In a saucepan over medium heat, add your unsalted butter to brown it. Stir frequently until the butter foams and then turns golden brown. Remove from heat and pour it into a mixing bowl. Let it cool for a few minutes, enjoying the nutty aroma that fills your kitchen.
In a medium bowl, whisk together the all-purpose flour, baking powder, and salt. This mixture will help create a light texture in your blondies.
Attach the bowl with the cooled brown butter to your stand mixer. Add the packed light-brown sugar and granulated sugar. Using the paddle attachment, mix on medium until the sugars and brown butter are well combined and creamy.
Crack in the 3 large eggs one at a time, beating on medium-high speed for about 3 minutes. The mixture should become light and fluffy. Be sure to scrape down the sides of the bowl with a spatula as needed.
Add the vanilla extract and mix until just combined.
Gradually add the flour mixture to the wet ingredients, mixing on low speed until just incorporated. Be careful not to overmix, as this can lead to denser blondies.
Fold in the butterscotch chips gently with a spatula. This ensures that the chips are evenly distributed without overworking the batter.
Spread the batter evenly into the prepared baking pan. Use a spatula to smooth the top for an even finish.
Bake the blondies in the preheated oven for 35 to 40 minutes. To check for doneness, insert a toothpick into the center. If it comes out clean with a few moist crumbs, they're ready. Avoid overbaking to keep them chewy.
Once baked, remove the pan from the oven and set it on a wire rack to cool completely. After cooling, lift the blondies from the pan using the parchment paper and cut them into squares to serve.