Preheat the oven to 350 degrees F. Line a 9-inch-square baking dish with foil, leaving a 2-inch overhang on two sides; lightly coat with cooking spray and set aside.
Whisk the flour, salt and baking powder in a small bowl. Melt the butter in a medium saucepan over medium heat and cook, swirling the pan occasionally, until it starts browning. Remove from the heat and whisk in the brown sugar and vanilla until dissolved; let cool slightly. Add the eggs and whisk until smooth. Stir in the flour mixture, then the apple and butterscotch chips. Pour into the prepared pan and smooth the top.
Bake the blondies until the edges are set and the top is lightly browned, about 25 minutes. Transfer to a rack and let cool completely in the pan. Lift out of the pan using the foil overhang and cut into pieces.