Preheat oven to 350 degrees. Lightly spray an 8x8 inch baking dish with cooking spray and line with parchment paper leaving a 1 inch over hang for easy transfer when blondies are done. Set aside.
Add melted butter and both light and dark brown sugar to a medium mixing bowl. Stir completely until combined. Add in egg and vanilla extract, stirring until combined. Batter should be smooth and have a caramel color. Add in dry ingredients: flour, baking powder, and salt. Stir until completely combined. Batter will be thick. Fold in chocolate chips and butterscotch morsels.
Spread blondie batter into baking dish. Spread a thin layer to fully cover the bottom of the baking dish. It may seem like there isn't enough but there is, the layer is just thin. Bake in the oven for 20 minutes, test with a toothpick inserted into the center and if it comes out clean the blondies are done. They may finish baking before 20 minutes depending on your oven.
Allow blondies to cool for 10 minutes before transferring to a cooling rack. After 10 minutes lift the blondies out of the baking dish by using the parchment over hand and place them on a cooling rack. Allow to cool for 10-15 more minutes. Once cool blondies are ready to cut and serve. Store any leftover in an airtight container.