Preheat the oven to 350 degrees F and spray a 9-inch square baking pan with cooking spray or butter it generously. For ease, I recommend lining the pan with parchment paper and spraying that, too.
In a medium bowl, whisk the flour, baking powder and salt.
In a small saucepan over medium heat, melt the butter and 1/4 cup of the butterscotch chips until the mixture is smooth. Transfer it to the bowl of a stand mixer.
Beat the brown sugar into the butter mixture, then the egg. Add the vanilla and bourbon and beat until combined. Add the flour mixture and beat until incorporated. Stir in the remaining 1/2 cup butterscotch chips.
Spread the batter into the prepared pan and bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out with not too much stuck to it. Let cool before cutting. Find this recipes and more in Duff Bakes: Think and Bake Like a Pro at Home ($27.50, William Morrow).