Preheat the oven to 350 degrees F. Line a 9x13-inch baking dish with parchment paper and spray with non-stick cooking spray, set aside.
In a medium-sized bowl stir together the flour, baking powder, and salt until combined, set aside.
In a large bowl add the brown sugar, melted butter, eggs, and vanilla and whisk together until smooth.
Add the dry ingredients to the wet and stir together until there are no dry patches.
Then, add 1 ½ cups of the butterscotch chips and fold them in until evenly distributed.
Spread the batter into the prepared baking dish, Take a handful of the remaining butterscotch chips and sprinkle it over the batter in the baking dish.
Place in the oven and bake for 25-30 minutes until a toothpick inserted into the center comes out clean.
Remove from the oven and let them cool completely in the pan.
Take the bars out using the parchment paper to help you lift them out. Cut into bars.
Place the remaining butterscotch chips into a microwave-safe bowl. Microwave in 15-second intervals, stirring in between until melted.
Place the melted butterscotch into a piping bag or ziptop bag and cut a small piece of the corner off. Drizzle over the cut bars, let them set for about 20 minutes so the butterscotch on top solidifies, then serve!