Melt the butter over medium heat in a medium stainless steel or light-colored skillet. Cook, stirring occasionally, until the butter smells nutty and small light-brown flecks have settled to the bottom of the pan, 6 to 8 minutes. Remove the pan from the heat, and pour the butter into a small bowl. Let cool 10 minutes.

Preheat the oven to 350°. Spray a 9-by-13-inch baking dish with nonstick cooking spray and set aside.

Stir together the flour, brown sugar, baking powder, and salt in a large bowl with a fork until combined. Add the melted butter, eggs, and vanilla; stir together until batter just comes together and there are no dry pockets of flour remaining. Fold in ½ cup of the pecans and 1 cup of the butterscotch or white chocolate chips.

Pour the batter into the prepared pan; spread into an even layer. Sprinkle the remaining ½ cup pecans and ½ cup chips evenly over the top of the batter. Bake until a wooden pick inserted in the center comes out clean, about 30 minutes.

Let blondies cool at least 30 minutes before slicing.